Further   Studies    of 

Ar-i   Their   Pollination 

Ey 
William  T«n&3ease 


UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


Further  Studies  of  Yuccas; 
aod  tlneir  Pollination. 

By  WILLIAM  TPELKASE. 

THE  FOURTH  ANNUAL  REPORT  OF  THK  MISSOURI   BOTANIC.U    > 
ISSUED,  MARCH  9,  1893. 


I 


FURTHER    STUDIES    OF  YUCCAS   AND     THEIR    POLLINATION. 

BY   WILLIAM   TRELEASE. 

Among  the  many  strange  things  brought  to  light  by 
biological  studies,  few  equal  in  interest  or  verge  so  closely  on 
the  improbable  as  those  which  concern  the  pollination  of 
the  Yuccas.  The  observed  facts,  chiefly  known  through 
the  work  of  Professor  Charles  V.  Riley  and  the  late  Dr. 
George  Engelmann,  have  been  admirably  summarized  by 
Professor  Riley  in  the  Third  Report  of  the  Garden.*  So 
far  as  direct  observation  on  pollination  is  concerned,  these 
refer  to  cultivated  specimens  of  Y.  filamentosa  and  glauca, 
the  latter  of  which  has  been  observed  also  in  the  wild 
state  in  Colorado  ;  f  but  the  collections  of  entomolo- 
gists, and  the  affected  fruits  of  the  Yuccas  of  various 
localities,  show  that  virtually  all  species  of  the  genus 
depend  for  their  principal  pollination,  if  not  altogether, 
upon  moths  of  the  Tineid  genus  Pronuba,  of  which  Riley 
has  characterized  three  species,  i  Professor  Riley,  there- 
fore, states  that  all  of  the  species  of  Yucca  native  east  of 
the  Rocky  Mountains  depend  for  their  pollination,  so  far 
as  is  now  known,  upon  a  single  species  of  Pronuba,  namely 
the  white  P.  yuccasella  ,§  while  the  tree  Yucca  of  the 
California  desert  and  the  adjacent  region,  Y.  brevifolia, 
is  pollinated  by  a  dingy  moth,  P.  synthetical  and  the 
aberrant  Yucca  W7iipplei,  which  Mr.  Baker  is  now  dis- 
posed to  place  in  a  distinct  genus  under  the  name  Hespero- 
yucca,  is  pollinated  by  an  equally  aberrant  spotted  moth, 
P.  maculata^  the  pollinating  actions  of  which  have  been 
briefly  reported  this  season  by  Coquillet.  *  *  Aside  from  this 


*  pp.  99  to  158,  pi.  34  to  43.  f  Riley,  I.  c.  124.  J  I.  c.  137. 

§  I.   c.   104,  121;    Proc.  Biological  Society  of  Washington,   vii.   94; 
Insect  Life,  iv.  369.  ||  I.  c.  121,  141.  f  ?.  c,  121,  139. 

**  Insect  Life,  iv.  370,  note. 

[181] 


252974 


182  MISSOURI   BOTANICAL    GARDEN. 

nothing  definite  has  been  made  known  concerning  either  the 
Pronubas  which  frequent  the  several  species  of  Yucca,  or 
their  mode  of  operation,  although  Riley  predicts  the  prob- 
able discovery  of  distinct  species  of  Prontiba  for  the  Mexican 
Y.  jilifera*  and  our  own  Y.  rupicola,]  Y.  Treculeana^ 
and  Y.  baccata.\ 

The  following  pages  contain  the  results  of  a  further  field 
study  which  I  have  been  enabled  to  make  during  the  spring 
of  1892,  through  the  interest  of  the  Board  of  Trustees  of 
the  Garden.  In  bringing  the  observations  together,  they 
have  been  arranged  under  the  respective  species  studied,  the 
classification  of  the  latter  being  substantially  that  employed 
in  the  detail  illustrations  of  the  last  volume.  § 

YUCCA. 

Filaments  nearly  or  quite  free  from  the  petals;  pollen  powdery ;  style 
stout,  not  capitately  expanded  nor  long-papillate,  with  a  rather  open  stig- 
matic  axile  canal;  fruit  baccate,  spongy,  or  capsular  with  septicidal  and 
apical-loculicidal  dehiscence. 

A.  SARCOYUCCA,  with  fleshy  fruits. 

r.  ALOIFOLIA,  L.  (PL  18).— According  to  Riley, ||  in- 
dividuals of  this  species  which  bloom  simultaneously  with 
Y.  filamentosa  along  the  southeastern  coast,  are  pollinated 
by  Pronuba  yuccasella.  The  species  is,  however,  quite 
unique  in  setting  good  fruit  rather  abundantly  in  cultiva- 
tion when  Pronuba  does  not  appear  to  be  present. If  This 
was  the  case  in  the  Garden  this  year,  when  the  species 

*  L  c.  131.  f  I.  c.  122.  J  Proc.  Biol.  Soc.  Washn.  vii.  96. 

I  Third  Report  Mo.  Bot.  Garden,  161.  ||  i.  c.  121. 

f  The  principal  references  to  the  fruiting  of  aloifolia  without  Pronuba 
are  the  following:  Deleuil,  Rev.  Horticole.-abst.  in  Gard.  Chron.  1880. 
siii.  807;  Engelmann,  Gard.  Chron.  1872,941,  Collected  Writings,  284 ; 
The  Garden,  fide  Tick's  Mag.  1880  and  Riley  in  Proc.  Amer.  Ass.  Adv. 
Sci.  xxix.  624;  Gardeners'  Chronicle,  1880,  xiii.  81;  Riley,  Third  Garden 
Report,  118  etc.;  J.  v.  V.  [van  Volxem],  Gard.  Chron.  1882,  xviii.  407. 
The  note  of  Layard  in  Nature,  xxii.  606,  may  perhaps  refer  to  this 
species,  though  the  species  is  not  named. 


FURTHER    STUDIES    OF   YUCCAS.  183 

bloomed  for  the  first  time  in  several  seasons,  and  a  number 
of  the  panicles  fruited  quite  freely.  The  earliest  of  these 
flowers  opened  as  the  last  flowers  of  filamentosa  were  fall- 
ing, so  that  it  was  supposed  at  first  that  they  were  pollin- 
ated by  P.  yuccasella,  which  had  been  observed  only  a  few 
days  previously,  but  this  supposition  was  not  substantiated 
by  the  discovery  of  the  moth  about  them,  or  of  its  larvae  in 
the  fruit. 

Professor  Kiley  has  shown  that  the  short  style  and  open 
stigma  of  aloifolia  appear  to  favor  self-pollination  when  the 
moth  is  not  present ;  but  a  study  of  our  plants  this  summer 
by  Mr.  Webber  and  myself  has  not  satisfied  either  of  us 
that  self  pollination  is  likely  to  occur  sufliciently  frequently 
to  explain  the  rather  abundant  fruiting  observed  here,  and 
in  the  case  of  a  single  panicle  covered  with  gauze,  no  fruit 
was  set  except  as  the  result  of  artificial  pollination.  The 
so-called  Yucca  hybrids  of  gardens  appear  for  the  most 
part  if  not  always  to  be  spontaneous  or  artificial  crosses 
between  the  variegated  and  other  forms  cultivated  under 
various  names,  but  now  generally  referred  to  this  species. 
Altogether  Y.  aloifolia  is  one  of  the  species  most  worthy 
of  study  in  its  native  habitat,  since  little  is  known  except 
that  it  sometimes  fruits  without  the  aid  of  Pronuba,  and 
that  its  seeds  sometimes  contain  the  larvae  of  P.  yuccasetta, 
while  the  exact  mode  of  pollination  when  the  moth  is 
excluded  is  not  known  from  observation. 

It  is  well  known  that  filamentosa,  when  cultivated  far 
north  of  its  range,  is  uncertain  in  its  blooming,  although 
further  south  it  flowers  every  year ;  and  attention  has  been 
called  frequently  to  the  periodicity  of  brevifolia  and  other 
species  in  their  native  home.*  No  doubt  this  is  connected 
with  the  previous  conditions  of  nutrition,  and  the  im- 
mediate climatic  influences  under  which  the  plants  have 
grown,  but  it  appears  quite  remarkable  that  so  many  plants 
of  aloifolia  at  the  Garden,  of  very  different  size  and  age, 


Riley,  L  c.  117. 


jg4  MISSOURI   BOTANICAL   GARDEN. 

should  have  bloomed  together  this  year,  after  a  long  period 
of  rest.* 

The  most  striking  morphological  peculiarities  of  the 
species,  aside  from  its  rather  stiff  sword-shaped  denticulate 
leaves,  are  the  marked  stipe  of  the  ovary,  and  the  decidedly 
hexagonal  cross  section  of  the  ripening  fruit,  due  to  the 
rapid  growth  of  the  nectar  grooves, —  both  of  which  feat- 
ures are  well  shown  on  plate  44  of  the  Third  Report. 

Y.  YUCATANA,  Engelm. —  So  far  as  I  can  learn,  nothing 
is  known  of  this  species  further  than  that  it  was  collected 
in  Yucatan  by  Schott,  whose  specimens  are  preserved  in  a 
few  herbaria. 

Y.  GUATEMALENSIS,  Baker  (PI.  1,  2,  19). — This  species  is 
said  to  occur  in  southern  Mexico,  as  well  as  Guatemala. 
In  August  and  September,  1892,  a  fine  plant,  said  to  have 
come  originally  from  Haage  and  Schmidt  as  a  Furcroea, 
bloomed  in  the  Garden,  synchronously  with  a  form  of 
gloriosa,  but  fully  a  month  later  than  aloifolia.  The  polli- 
nation arrangements  appear  to  be  almost  identical  with  those 
of  baccata,  which  are  described  below.  In  this  specimen  the 
scptal  nectar  glands,  although  they  are  not  very  large,  were 
more  active  than  those  of  any  other  true  Yucca  known  to 
me,  and  their  secretion  appeared  in  rather  copious  drops  at 
the  base  of  the  ovary,  where  the  nectar  grooves  open,  or 
in  smaller  drops  near  its  top,  where  the  glands  open  into 
the  grooves,  if,  as  frequently  happens,  the  latter  have 
spread  somewhat.  Artificial  pollination  gave  a  number  of  the 
very  large  pendent  baccate  fruits,  but  nothing  is  known  of 
the  natural  pollinators  of  the  species. 

The  fruit  raised  by  artificial  pollination  is  very  stout. 
One  of  the  larger  (but  not  the  largest)  of  the  specimens 
measured  2X3£  in.  and  weighed,  while  still  green,  6  oz. 
At  first  quite  hexagonal  in  cross  section,  its  intercarpellary 
facets  ultimately  disappear  toward  the  base.  The  bases  of 
the  filaments  are  adherent  to  the  base  of  the  fruit,  much 

*  Meehan  (Monthly,  ii.  190)  mentions  a  plant  which  flowered  for  the 
first  time  when  at  least  seventy-five  years  old. 


FURTHER   STUDIES    OF   YUCCAS.  185 

as  in  aloi folia,  and  similarly  reflexed.  When  fully  grown, 
but  not  ripe,  the  fruit  is  of  a  clear  apple-green  color. 

Y.  SCHOTTII,  Engelm.  (  Y.  macrocarpa,  Engelin.)  (PI. 
3).  —  Though  Y.  macrocarpa ,  which  appears  to  be  only 
this  species,  is  not  uncommon  in  parts  of  southern  Arizona, 
no  observations  have  been  made  on  its  pollination,  and  I 
was  unable  to  find  it  in  bloom.  Flowers  collected  in  the 
Santa  Kita  Mountains,  July  9,  1881,  and  in  the  Huachuca 
Mountains  in  September,  1882,  show  either  an  unusual  dura- 
tion of  the  flowering  period,  or  great  variability  in  it. 
Y.  elata  and  Y.  baccata,  which  are  spring-blooming  species 
of  the  same  region,  are  pollinated  by  Pronuba  yuccasella, 
which  can  scarcely  be  expected  to  occur  as  late  as  the  dates 
mentioned;  but  baccata,  in  different  localities,  is  known  to 
have  a  prolonged  period  of  blossoming  comparable  with 
that  of  the  different  forms  of  filamentosa  in  the  southeast, 
so  that  it  is  possible  that  in  its  pollination  arrangements 
Schottii  bears  the  same  relation  to  baccata  that  the  autum- 
nal gloriosa  does  to  filamentosa . 

Y.  TRECULEANA,  Carr.  (PI.  18).— This  Texan  and 
Mexican  species  is  believed  by  Riley  to  be  pollinated  by  a 
probably  distinct  Pronuba,*  but  no  observations  have  been 
made  on  it.  A  specimen  which  bloomed  in  the  Garden  this 
season  was  quite  as  sterile  as  other  cultivated  Yuccas  aside 
from  filamentosa  and  glauca,  which  are  pollinated  by 
P.  yuccasella,  and  the  aloifolia  noted  above;  and  this 
has  been  the  case  on  the  several  occasions  when  the  speci- 
men has  bloomed  in  the  past. 

According  to  Engelmann  f  Treculeana  is  reported  by 
Lindheimer  as  sterile  in  Texan  gardens,  though  the  wild 
plants  are  abundantly  fertile. 

Y.  BACCATA,  Torr.  (PI.  20). — With  the  possible  exception 
of  Y.  glauca,  this  is  the  most  widely  distributed  of 
our  species,  ranging  in  a  variety  of  forms  from  southern 
Colorado  into  Mexico  and  to  California,  where  it  extends 

*  I.e.  122;  Proc.  Biol.  Soc.  Washn.  vii.  96;  Insect  Life,  iv.  371. 
t  Collected  Writings,  284. 


186  MISSOURI    BOTANICAL    GARDEN. 

from  about  Monterey  into  the  peninsula.  It  therefore 
connects  the  territory  of  glauca,  which  is  pollinated  by 
Pronuba  yuccasetta,  with  that  of  two  Calif ornian  species 
pollinated  by  very  distinct  moths.  No  observations  appear 
to  have  been  made  heretofore  on  its  pollination,  nor  has 
any  Pronuba  been  taken  on  its  flowers,  but  Professor  Riley 
predicts  the  probable  discovery  of  a  distinct  species  for  it.* 
In  the  valley  between  San  Bernardino  and  Colton,  Cali- 
fornia, baccafa  is  found  in  some  abundance,  but  no  Pronuba 
Avas  seen  in  any  of  the  specimens  examined  about  the  mid- 
dle of  April,  when  they  were  in  full  bloom,  and  they  are 
said  never  or  very  rarely  to  fruit  there,  by  Mr.  S.  B.  Parish, 
in  whose  company  my  observations  on  this  occasion  were 
made. 

About  Banning  and  Cabazon,  on  the  western  edge  of  the 
Colorado  desert,  where  the  plants  are  more  abundant  and 
of  larger  size,  often  with  a  trunk  five  or  six  feet  high, 
they  are  more  generally  fertile,  and  a  quantity  of  fruits  of 
the  preceding  year  were  collected  from  the  crowns  of 
leaves  into  which  they  had  fallen  on  maturity,  and  where 
they  had  been  protected  from  rodents.  Most  of  these 
fruits  were  strongly  constricted  about  the  middle,  and  per- 
forated in  places,  where  the  larvae  of  a  Pronuba  had 
escaped.  The  plants  were  not  blooming  very  freely  this 
year,  but  several  specimens  of  a  white  Pronuba  were  taken 
resting  in  the  flowers,  and  though  numerous  panicles  had 
bloomed  without  setting  any  fruit,  others  were  sparingly, 
and  still  others  abundantly,  fertilized,  and  the  ovaries  of 
the  fertilized  flowers  showed  unmistakable  constrictions  or 
indentations  indicative  of  the  opposition  of  Pronuba;  still, 
the  moths  were  not  sufficiently  numerous  to  render  night 
observations  on  their  work  possible. 

A  number  of  blooming  plants  of  baccata  were  examined 
about  the  first  of  May  on  the  mesas  back  of  San  Diego, 
where,  notwithstanding  the  more  southern  latitude,  the 

*  Proc.  Biol.  Soc.  Washington,  vii.  96. 


FURTHER   STUDIES   OF   YUCCAS.  187 

season  is  later  than  on  the  desert  and  in  the  warmer  valleys 
further  north.  On  this  occasion  I  was  accompanied  by  Mr. 
C.  R.  Orcutt,  who  informs  me  that  the  seeds  of  baccata  are 
in  some  seasons  very  much  eaten  by  larvae,  probably  of 
Pronuba ;  *  and  the  cluster  of  perforated  fruits  figured  on 
the  accompanying  plate  was  photographed  many  years  ago 
in  the  same  region.  Though  the  oldest  pistils  were  less 
developed  here  that  at  Cabazon,  there  was  abundant  evi- 
dence that  they  had  been  oviposited  in  by  Pronuba, 
several  individuals  of  which  were  taken  in  the  flowers. 

The  flowers  of  this  Yucca,  though  they  are  as  variable 
in  form  as  those  of  the  eastern  capsular  species,  agree,  so 
far  as  I  have  observed,  in  having  the  sepals  decidedly  um- 
bonate  at  the  base,  as  is  also  frequently  the  case  with 
aloifolia,  so  that  each  flower  appears  somewhat  as  if  con- 
stricted immediately  above  the  bottom.  In  color  they 
range  from  creamy  white,  often  with  a  tinge  of  green,  to  a 
decided  brown  purple,  the  perianth  being  always  very  glossy, 
and  they  are  slightly  and  delicately  fragrant.  The  mi- 
nutely papillate  filaments  vary  much  in  length,  but  com- 
monly reach  to  about  the  base  of  the  style,  where  they  are 
more  or  less  abruptly  thickened  and  bent  outwards.  In 
one  observed  case,  however,  they  were  as  long  as  the  entire 
pistil.  A  curious  feature  observed  in  dried  specimens  as 
well  as  in  recently  fertilized  flowers  with  drying  stamens, 
is  the  strong  recurving  of  the  upper  part  of  the  filaments 
shown  on  plate  48  of  the  last  Report,  but  never  observed 
in  fresh  unfertilized  flowers,  as  it  of  ten  is  in  Y.  Treculeana. 

The  anthers  do  not  appear  to  dehisce  quite  as  promptly 
as  in  the  filamentosa  group,  where  there  is  practically  no 
dichogamy,  so  that  in  this  species  the  Pronuba  is  more 
likely  of  necessity  to  have  derived  her  load  of  pollen  from 
another  flower  when  she  begins  pollination  on  one  which  is 
newly  expanded ;  but  the  protogyny  noted  scarcely  extends 
beyond  the  evening  on  which  the  flower  opens,  so  that  it  is 

*  Specimens  of  old  fruit  received  since  the  above  was  written  are 
badly  infested  by  an  undetermined  beetle. 


138  MISSOURI    BOTANICAL    GARDEN. 

by  no  means  as  effective  in  preventing  close  fertilization  as 
in  brevijotia  and  Whipplei,  which  are  described  below. 
The  bright  golden  yellow  pollen  is  readily  seen  on  any  part 
of  the  flower  in  contact  with  which  it  may  have  come,  and 
particularly,  on  the  nearly  white  ovary  and  the  pure  white 
style. 

The  latter  is  not  usually  as  long  as  in  the  flower  figured 
in  the  last  Report  and  already  referred  to.  It  has  a  very 
open  stigmatic  tube  which  passes  into  the  upper  ends  of  the 
ovarian  cells,  as  may  be  seen  in  some  cases  even  by  looking 
down  the  wide  channel  with  the  aid  of  a  hand  lens,  for  there 
is  little  stigmatic  secretion.  In  this  species  it  is  also  very 
easy  to  convince  oneself  that  the  three  pollen-conducting 
grooves,  similar  to  those  figured  by  Webber  for  glauca* 
but  also  seen  in  Agave  and  other  plants  with  this  type 
of  pistil,  are  formed  by  the  uppermost  part  of  the  infolded 
edges  of  the  carpels,  which  further  down  coalesce  to  form 
the  true  septa,  and  constitute  the  placentae.  As  in  other 
Yuccas,  each  septum  of  the  ovary  contains  a  nectar  gland  ;t 
but  the  glands  of  baccata  are  not  so  large  and  open  as  in 
the  Jilamentosa  group  of  species,  in  this  respect  agree- 
ing with  those  of  the  other  fleshy-fruited  Yuccas  that  I 
have  examined.  Notwithstanding  this,  they  appear  to  be 
rather  more  active  than  in  the  former  group  (herein 
agreeing  with  Guatemalensis  among  the  baccate  species, 
gloriosa  among  the  spongy-fruited  species,  and  the  Hespero- 
yuccas),  their  secretion  sometimes  appearing  in  small 
quantity  at  the  base  of  the  pistil,  where  their  large  ducts  dis- 
charge. Several  of  the  flowers  examined  at  San  Diego  in 
the  morning  were  very  wet  on  the  outside,  a  condition  which 
has  been  observed  on  other  species  ;J  but  though  it  is 

*  American  Naturalist,  1892,  303,  309,  pi.  13,  f.  38. 

t  Trelease:  Bulletin  of  the  Torrey  Bot.  Club,  1886, 135,  and  Third  Gar- 
den Report,  pi.  63;  Riley,  L  c.  109,  Proc.  Biol.  Soc.  Washington,  vii.  91, 
and  Insect  Life,  iv.  364  to  366. 

J  Y.ftlamentosa,—  Meehan,  Proc.  Phila.  Acad.  1888,  276,  and  Trelease, 
Third  Garden  Report,  123 ;  Y.  gloriosa,—  Meehan,  Proc.  Phila.  Acad.  1880, 
355,  1883,  191 ;  and  Hesperoyucca,  mentioned  below. 


FURTHER   STUDIES    OF   YUCCAS.  189 

pretty  clear  that  this  fluid  is  not  derived  from  the  septal 
glands,  its  source  is  not  evident. 

A  number  of  small  beetles  and  flies  visit  the  flowers, 
apparently  attracted  by  the  pollen,  which  in  some  cases 
they  have  been  seen  to  eat.  As  was  noted  last  year  for 
glauca*  these  insects  sometimes  dislodge  masses  of 
pollen  from  the  anthers,  and  the  length  of  the  stamens  in 
baccata  may  frequently  cause  some  of  this  to  fall  upon  the 
tips  of  the  stigmatic  lobes.  In  one  case  a  small  mass  of 
pollen  was  found  in  this  position,  and,  in  another,  some 
pollen  had  been  pushed  into  the  mouth  of  the  stigmatic 
chamber,  evidently  having  fallen  upon  the  petals  and  been 
transferred  to  the  stigma  by  the  pressure  of  my  hand  as  I 
gathered  the  flower.  In  some  such  way,  therefore,  perhaps 
exceptional  pollination  may  be  effected  now  and  then  in 
baccata  when  Pronuba  is  not  present ;  but  I  should  not  ex- 
pect this  to  be  of  frequent  occurrence,  and  the  observations 
at  Colton  show  that  it  must  be  rare  or  ineffective. 

The  moths  taken  in  the  flowers  of  this  species  at  Cabazon 
and  San  Diego  are  somewhat  larger  than  many  specimens 
of  Pronuba  yuccasella,  and  they  appear  to  have  the  tip  of 
the  abdomen,  the  maxillary  palpi,  and  the  antennae,  as  well 
as  the  chitinized  parts  in  general  when  denuded,  a  little 
darker  in  color,  but  aside  from  these  and  the  greater  ease 
with  which  their  scales  are  rubbed  off,  I  can  detect  no 
characters  by  which  they  can  satisfactorily  be  separated 
from  P.  yuccasella  of  the  Mississippi  Valley  and  Rocky 
Mountains,  which  is  also  said  to  be  indistinguishable  from 
the  moth  of  the  Gulf  region. f  Like  the  eastern  representa- 
tives of  yuccasella  they  rest  within  the  flowers  during  the 
day,  with  their  heads  directed  toward  the  base  of  the 
stamens,  though  they  seem  a  little  more  ready  to  drop  from 
the  flowers  when  disturbed.  Unfortunately  I  have  been 
able  to  make  no  observations  on  their  work,  but  the 
females  bear  loads  of  pollen  of  the  usual  form,  and  fertil- 

*  Cf.  Riley,  I.  c.  125. 

t  Professor  Riley  has  since  confirmed  this  conclusion. 


jg0  MISSOURI   BOTANICAL    GARDEN. 

ized  flowers  show  conclusively  that  they  thrust  this  well 
into  the  stigmatic  canal, —  in  some  cases  apparently  even 
into  the  top  of  the  ovarian  cells,  which,  owing  to  the  short 
style  and  the  deep  stigmatic  notches,  they  can  reach  easily 
with  their  long  maxillary  tentacles.  In  ovipositing,  they 
doubtless  back  down  between  the  upper  ends  of  the 
stamens,  and  the  ovary  is  pierced  at  about  its  middle.  The 
septa,  and  the  median  line  of  each  cell  (which  is  produced 
into  the  cell  as  a  false  dissepiment,  dividing  the  cell  into 
two),  being  covered  by  the  appressed  lower  part  of  the  fila- 
ment, the  moth  is  constrained  to  puncture  the  wall  part 
way  between  the  true  and  false  partitions,  as  she  commonly 
does  in  filamentosa,*  this  being  also  its  thinnest  part.  At 
San  Diego,  where  the  moths  were  more  abundant  than  at 
Banning,  as  many  as  three  to  five  punctures  in  a  vertical 
series  were  seen  several  times  in  one  cell  of  an  ovary,  the 
other  cells  sometimes  showing  none  at  all. 

The  compound  microscope  reveals  the  presence  of  pollen 
in  the  stigmas  of  all  such  flowers  punctured  for  oviposition 
as  I  have  examined,  and  a  hand  lens  commonly  shows  it, 
though  not  always.  The  open  stylar  canal  is  frequented 
by  large  numbers  of  a  white  Thrips,  which  sometimes  pene- 
trate into  the  cells  of  the  ovary,  and  doubtless  scatter 
the  pollen  greatly,  perhaps  devouring  some  of  it.  On  dried 
fruits  of  the  preceding  season,  the  perforations  made  by 
escaping  larvae  are  commonly  elevated,  the  uninjured  tissue 
evidently  shrinking  more  in  drying  than  that  immediately 
surrounding  the  tunnel  of  the  larva.  These  dried  fruits 
sometimes  show  constrictions  corresponding  to  the  points 
of  oviposition,  but  they  are  frequently  obliterated  in  the 
development  of  the  pulpy  exocarp. 

Y.  AUSTRALIS,  (Engelm.).  (PI.  4,  5).  — A  study  of 
material  on  the  Sierra  Blanca  plateau  of  southwestern 
Texas,  and  a  careful  review  of  the  literature  of  the  species 
related  to  baccata,  enables  me  to  fix  without  further  ques- 

*  Riley,  1.  c.  pi.  36,  f.  2. 


FURTHER   STUDIES    OF   YUCCAS.  191 

tion  the  namej£Zt/§ra  for  the  large  Mexican  "  palma  "  with 
drooping  panicle,  for  it  has  satisfied  me  that  the  greater 
part  of  Engelmann's  Yucca  baccata,  var.  australis  consists 
of  another  form  (from  which  perhaps  one  other  species  with 
erect  panicle,  in  the  upper  Mexican  plateau,  may  be  sepa- 
rated ultimately).  Y.  australis  is  the  large  Yucca 
collected  by  Thurber  about  Parras,  Coahuila,  in  November, 
1852  (no.  1857,  in  Herb.  Torrey.),*  and  said  to  become 
sometimes  thirty  feet  high  and  two  or  three  feet  in 
diameter,  by  Bartlett,f  who  figures  a  much  branched  large 
specimen.  It  is  also  mentioned  by  Baker  in  the  Gar- 
deners' Chronicle  for  1870,  p.  1088,  under  the  number 
26,  but  without  name;  and  by  Engelmann  (cf.  Col- 
lected Writings,  p.  292),  as  a  variety  under  baccata.  So 
far  as  I  can  judge  from  herbarium  material,  it  was 
collected  in  Mexico  by  Coulter  (no.  1571  in  Hb.  Gray.), 
and  it  appears  to  be  the  plant  collected  in  the  Carneros 
Pass,  Coahuila,  by  Pringle  in  1889  (no.  2841 )  and  1891  (no. 
3912).  It  appears,  therefore,  to  be  a  species  of  the 
northern  high  lands  of  Mexico,  extending  into  the  elevated 
Sierra  Blanca  region  of  Texas,  where  it  is  associated  with 
other  southern  plants  like  Agave  applanata  and  A.  Posel- 
gerii.  Its  nearest  described  allies,  which  Mr.  Baker  tells 
me  have  narrow  leaves,  are  Y.  periculosa,  Baker,  and  Y. 
circinata,  Baker,  both  of  which,  like  the  present  species, 
have  been  referred  usually  to  baccata,  and  which  are  yet 
imperfectly  known. 

Seedling  plants  have  the  blue-green  leaves  of  Treculeana, 
and  possess  a  cluster  of  rather  fleshy  fusiform  roots  be- 
coming as  thick  as  one's  finger,  but  no  central  tap  root. 
With  age  these  roots  are  replaced  by  long,  tough,  cord-like 
roots  as  thick  as  a  lead  pencil.  The  trunks  at  length  be- 
come a  foot  or  two  thick,  and  generally  from  ten  to  fifteen 
feet  high,  where  my  observations  were  made.  Though 


*  Torrey,  Bot.  Mex.  Bound.  221-2. 
t  Personal  Narrative,  ii.  490. 


192  MISSOURI    BOTANICAL   GARDEN. 

commonly  unbranched  or  with  only  a  double  crown,  they 
sometimes  develop  several  large,  more  or  less  spreading 
branches.  The  very  concave  leaves  are  of  a  clear  green 
color,  and  either  entirely  smooth  to  the  touch  or  only 
slightly  scabrous  on  the  few  angles  which  sometimes  run 
longitudinally  on  the  back.  Their  margin  on  unfolding  is 
entire,  purplish  brown,  and  dilates  into  the  firm  but  blunt 
brown  tip,  from  which,  after  the  leaves  have  expanded,  it 
breaks  away  in  the  form  of  numerous  stout  gray  or  brown- 
ish fibers,  pectinately  spreading  near  the  apex,  and  becom- 
ing longer  and  more  remote  below,  so  that  ultimately  the 
leaves  are  not  filif  erous  except  for  a  few  crowded  short  fibers 
immediately  below  the  point,  and  a  more  or  less  abundant 
aggregation  of  loose  threads  between  their  bases,  causing  a 
cobwebby  appearance.  The  older  leaves  for  a  long  time  are 
reflexed  against  the  trunk,  and  appear  to  be  more  fibrous 
and  rigid  than  those  of  Schottii  and  baccata.  The  inflores- 
cence is  ample,  recalling  that  of  Treculeana,  and  the  con- 
spicuous white  bracts  sometimes  measure  as  much  as  3X12 
inches. 

In  the  Texan  region  indicated,  this  form  grows  with 
Yucca  elata,  baccata  being  absent;  but  it  blooms  a  full 
month  earlier  than  the  associated  species.  Its  fruit,  like 
that  of  several  of  the  other  baccate  species,  is  usually 
long  beaked,  and  the  seeds  are  tunneled  in  the  manner 
characteristic  of  the  work  of  Pronuba,  the  pulp  being  per- 
forated by  the  escaped  larvae.  I  was  unable  to  study  this 
species  in  bloom,  but  large  fruits  gathered  some  three 
weeks  after  fertilization  show  none  of  the  constrictions  or 
indentations  which  so  commonly  mark  the  ovipositing  punc- 
tures of  the  Pronuba  moths,  which  leads  to  a  suspicion  that 
the  eggs  may  be  deposited  in  the  upper  part  near  the  stigma. 

Y.  VALIDA,  Brandegee.  —  In  admitting  this  species  to  the 
list  of  Yuccas  published  in  the  Third  Report,  I  had  over- 
looked the  fact  that  Mr.  Brandegee*  himself  has  referred 

*  Proc.  Calif.  Acad.  (2),  iii.  175. 


FURTHER    STUDIES    OF    YUCCAS.  193 

it  to  baccata.  The  smooth  leaves  of  the  specimens  I  have 
seen  are,  however,  quite  unlike  the  rough  foliage  of  the 
usual  northern  form  of  baccata,  and  the  question  of  the  dis- 
tinctness of  valida  may  still  be  kept  open.  I  think  it  very 
probable  that  it  will  be  found  in  the  heart  of  Mexico,  where 
several  little-studied  Yuccas  of  the  baccata  set  occur,  as 
well  as  in  its  present  range  on  the  peninsula  of  Lower  Cali- 
fornia. Nothing  is  known  of  its  pollination. 

Y.  FILIFERA,  Chab.  — Nothing  is  known  of  the  pollina- 
tion of  this  Mexican  tree  Yucca,  except  that  herbarium 
specimens  of  its  fruit  show  the  work  of  Pronuba  larvae, 
from  which  Professor  Kiley  infers  that  a  large  and  interest- 
ing species  of  moth  peculiar  to  it  will  be  discovered.* 

B.  CLISTOYUCCA,  with  leathery  or  spongy  indehiscent  fruits . 

Y.  BREVIFOLIA,  Engelin.  (PI.  6-9,  21)f . — This,  our  largest 
tree  Yucca,  is  interesting  from  several  points  of  view. 
Seedlings  possess  decidedly  glaucous  flexible  leaves,  rather 
similar  to  those  of  young  WJiipplei.  At  first  a  fleshy 
round-pointed  caudex  develops  below  ground,  from  which 
long  simple  tough  roots  spread  in  all  directions ;  but 
this  original  descending  axis  disappears  with  age,  so  that 
the  old  tree  has  a  flat  or  irregular  basal  disk,  from  which 
the  tough  roots,  now  as  thick  as  a  lead  pencil,  run  into  the 
soil  for  a  long  distance.  As  a  rule  each  plant  forms  only  a 
single  trunk,  but  occasionally  laterals  develop,  generally  as 
a  result  of  injury  to  the  main  stem.  Until  it  is  eight  or 
ten  feet  high,  the  trunk  is  unbranched,  and  covered 
throughout  with  the  very  rough  and  rigid,  mostly  yellowish- 
green  leaves,  the  lower  of  which  are  reflexed.  When  of 
about  this  size,  it  blooms  for  the  first  time  (PL  6),  after 

*  I.  c.  121;  Proc.  Biol.  Soc.  Washn.,  vii.  96;  Insect  Life,  iv.  371.  As 
a  further  reference  to  this  species  should  be  given  Fenzi:  Boll.  Soc. 
Tosc.  ortic.  xiv.  1889,  278,  with  plate. 

f  See  an  article  by  Shinn,  on  "The  Land  of  the  Tree  Yuccas,"  in 
American  Agriculturist,  1891,  689. 

13 


194 


MISSOURI   BOTANICAL    GARDEN. 


which  two  or  three  stout  branches  usually  develop  by  the 
side  of  the  original  apex,  which  now  has  ended  its  growth. 
When  these  have  reached  a  length  of  two  or  three  feet 
each  forms  a  terminal  inflorescence,  and  branches  in  its 
turn,  in  this  way  giving  rise  to  a  repeated  forking  or 
tripartition.  On  an  overturned  trunk,  however,  several  of 
the  stronger  branches  usually  become  erect  and  grow  to  a 
height  equal  to  that  of  young  trees,  before  blooming  and 
branching  (PI.  8),  but  so  far  as  I  have  seen  they  do  this 
without  forming  roots  of  their  own,  their  supply  of  food 
and  moisture  coming  through  the  persistent  roots  of  the 
main  trunk.*  On  the  large  stems,  and  even  on  some  of  the 
larger  branches  of  old  trees,  the  reflexed  leaves  gradually 
fall  away,  and  expose  to  view  a  very  thick  gray  bark,  deeply 
fissured  into  quadrangles  measuring  about  1X2  inches. 
As  the  trunks  increase  in  height  they  also  become  much 
thicker,  the  loosely  fibrous,  water-soaked  wood  being  marked 
in  concentric  rings,  resembling  those  of  Dicotyledons  and 
Conifers,  f  At  the  base,  these  older  trees  dilate  quite 
abruptly,  from  the  development  of  a  circle  of  thick  con- 
fluent roots,  which  correspond  to  those  so  commonly  seen  in 
the  form  of  more  or  less  marked  prolongations  of  ridges 
and  buttresses  on  Dicotyledons,  and  constitute  the  root- 
bearing  disk  mentioned  above  (PI.  9).  These  large  roots 
possess  a  structure  superficially  similar  to  that  of  the  trunk. 
When  preparing  to  flower,  this  is  one  of  the  most 
attractive  of  all  the  Yuccas,  the  ovoid  inflorescence  buds, 
each  as  large  as  an  ostrich  egg,  being  closely  invested  by 
large  thick  white  bracts,  after  the  manner  of  a  banana 
inflorescence ;  but  the  bracts  soon  become  dry  and  crum- 
bling, and  the  expanded  cluster,  though  of  very  compact 


*  An  excellent  wood  cut  showing  this  habit  of  growth  occurs  in  the 
Gray  Herbarium,  evidently  clipped  from  one  of  the  English  horticultural 
journals,  but  I  have  been  unable  to  obtain  a  more  exact  reference  to  it. 

t  The  structure  and  mode  of  thickening  in  arborescent  Liliacese  is  very 
iully  treated  by  Roseler  in  Pringsheim's  Jahrb.  f.  wiss.  Bot.  1889,  xx. 
l>92-348,  with  several  plates. 


FURTHER   STUDIES    OF   YUCCAS.  195 

habit,  is  of  an  inconspicuous  greenish  white,  and  possesses 
an  odor  which  is  so  oppressive  as  to  render  the  flowers 
intolerable  in  a  room,  although  the  usual  designation  of 
fetid  is  not  strictly  accurate.*  Though  the  flowers  differ 
somewhat  from  the  common  Yucca  form,  they  are  quite  as 
variable  as  those  of  other  species  of  the  genus,  and  range 
from  globose  to  nearly  oblong,  or  even  prismatically  pyri- 
form  when  first  opening.  The  petals  differ  from  those  of 
other  species  in  being  very  thick,  sometimes  measuring  as 
much  as  a  quarter  of  an  inch,  and  correspondingly  rigid, 
and  on  different  plants  they  vary  from  glabrous  to  very 
pubescent,  and  from  glossy  to  quite  dull,  but  usually  with 
the  waxen  appearance  so  commonly  seen  in  the  genus. 

The  filaments  here  are  generally  much  shorter  than  the 
pistil,  against  which  they  are  very  closely  applied  except 
near  the  top,  where  they  are  often  clavately  thickened,  and 
the  lower  part  is  usually  villous  papillate.  The  pale  lemon 
yellow  anthers  differ  strikingly  from  those  of  eastern  spe- 
cies, and  in  degree  from  those  of  other  Calif ornian  Yuccas, 
in  dehiscing  only  some  forty-eight  hours  after  the  flower 
has  opened,  while  the  stigma  appears  to  be  fully  receptive 
at  the  time  of  first  expansion. 

The  whitish-green  almost  conical  pistil  is  destitute  of  a 
clearly  marked  style  such  as  baccata  and  filamentosa  show, 
but  its  upper  part  is  not  occupied  by  the  ovarian  cells,  and 
so  is  virtually  stylar.  The  lobing  between  the  carpels  at 
top  is  so  slight  that  the  stigma  is  almost  equally  6-notched. 
The  stylar  canal  is  rather  ample  above,  but  its  connection 
with  the  ovarian  chanibers  is  through  a  series  of  slits, 
rather  than  open  pores,  and,  at  least  after  pollination,  the 
passages  are  often  occluded  by  the  conducting  tissue.  The 
septal  nectar  glands  are  less  developed  in  this  species  than 
in  any  other  which  I  have  studied.  They  are  always  nar- 
row, and  in  some  cases  do  not  reach  below  the  upper  third 


*  Cf.  Parry,  Amer.  Naturalist,  fc*.  141 ;  abst.  in  Gardeners'  Chronicle, 
».  s.  iii.  492. 


196  MISSOURI    BOTANICAL    GARDEN. 

of  the  ovary.  Externally  they  open  in  the  usual  manner , 
but  the  deep  outer  septal  grooves  are  little  if  at  all  expanded 
into  a  conducting  channel,  though  they  reach  to  the  base 
of  the  pistil  in  the  usual  manner  and  expand  there  into 
triangular  spaces.  I  have  not  observed  any  evidence  that 
the  septal  glands  secrete  at  all,  nor  is  the  stigmatic  secretion 
as  abundant  here  as  in  most  species. 

The  dark  colored  Pronuba  synthetica,  which  Professor 
Kiley  *  describes  as  peculiar  to  this  Yucca,  rests  during  the 
day  within  the  flowers  in  much  the  position  already  de- 
scribed for  the  eastern  P.  yuccasella,  or,  especially  when 
disturbed,  retires  between  the  densely  crowded  flowers, 
where  it  is  protected  from  most  dangers ;  but  it  is  more 
active  through  the  day  than  its  eastern  congener.  Towards 
evening  the  moths  become  quite  active,  and  it  is  probable 
that  copulation  of  the  sexes  occurs  before  night,  for  I  have 
not  seen  male  moths  at  night  within  the  flowers  where  the 
females  were  occupied  in  oviposition.  There  is  also  reason 
to  believe  that  the  latter  accumulate  their  loads  of  pollen  at 
an  early  hour,  though  this  again  is  only  inference,  since  I 
have  not  witnessed  the  operation,  even  in  the  cases  in 
which  I  have  suspected  that  a  moth  was  so  employed,  owing 
to  the  peculiarly  closed  condition  of  the  flowers.  Unlike 
the  other  known  species,  this  Pronuba  appears  slow  to  take 
flight.  Though  it  is  easily  disturbed,  so  as  to  run  about 
and  seek  concealment  between  the  flowers,  I  have  seen  it 
take  to  the  wing  only  a  few  times,  and  then  it  merely  sailed 
down  to  the  ground,  not  far  from  the  tree.  This  apparent 
indisposition  to  leave  the  flowers  may,  perhaps,  be  con- 
nected with  the  almost  constant  occurrence  of  high  winds 
on  the  desert.  Whatever  its  cause,  this  habit  of  the  moths 
appears  to.  restrict  cross-pollination  to  flowers  of  the  same 
plant  more  closely  than  is  the  case  with  other  Yuccas, 
though  there  must  be  frequent  flights  from  plant  to  plant 

*  1.  c.  121,  141;  Proc.  Biol.  Soc.  Washington,  vii.  94;  Insect  Life,  iv. 
370.  (This  was  first  called  P.  paradoxa,  but  without  description.— Riley 
Proc.  Wash.  Ent.  Soc.  1888,  i.  154,  and  Insect  Life,  i.  372. 


FURTHER    STUDIES    OF    YUCCAS.  197 

in  quiet  weather,  and  especially  at  night,  when  the  wind 
sometimes  falls;  and  the  development  of  the  stigma  two 
days  in  advance  of  the  stamens  of  a  given  flower,  renders 
close  fertilization  in  the  strictest  sense  improbable. 

The  light  yellow  pollen  is  in  such  marked  contrast  with 
the  smoky  tint  of  the  moth,  that  laden  females  are  recog- 
nizable from  a  considerable  distance,  and  notwith standing 
the  failure  of  direct  observation,  there  is  every  reason  to 
believe  that  the  latter  collect  their  burden  from  the  older 
flowers  with  the  same  deliberateness  that  has  been  observed 
in  the  other  known  species  of  Pronuba,  since  it  is  held 
under  the  well  developed  tentacles  in  the  same  manner  as 
by  them. 

On  first  examining  the  flower  clusters  of  brevifolia,  I 
was  impressed  by  the  remarkable  symmetry  of  most  of  the 
fertilized  pistils,  some  of  wThich  had  already  reached  half 
the  size  of  the  mature  fruit,  which  is  in  marked  contrast 
with  the  constriction  or  indentation  of  the  eastern  capsular 
Yuccas  at  the  point  where  the  ovary  has  been  punctured  in 
oviposition.  This  absence  of  deformity  was  explained, 
however,  when  the  act  of  oviposition  was  witnessed,  for 
the  moth  pierces,  in  this  species,  the  uppermost  part  of  the 
style,  conveying  its  eggs  down  to  the  ovary  through  the 
stylar  channel, —  the  course  followed  by  the  pollen  tubes. 

The  female  of  most  species  of  Pronuba  seeks  for  a  fresh 
flower  in  which  to  deposit  her  eggs,  showing  preference  for 
one  in  the  first  night  of  expansion.  To  this  she  is  probably 
impelled  by  the  impulse  to  insure  for  her  offspring  a  suf- 
ficient supply  of  food,  the  younger  flowers  being  less  likely 
than  the  older  to  be  already  overstocked  with  eggs.  This 
instinct  is  particularly  marked  in  P.  synthetica,  which  I 
have  never  seen  ovipositing  in  any  but  the  youngest  flowers, 
while  I  have  repeatedly  seen  the  pollen-laden  moths  force 
themselves  into  the  very  narrow  clefts  between  the  rigid 
sepals  of  an  opening  bud,  their  flattened  form  facilitating 
this,  after  which  only  the  most  fragmentary  glimpses  of 
their  work  were  possible.  But  during  something  over  a 


198  MISSOURI   BOTANICAL    GARDEN. 

week  in  the  early  part  of  April,  spent  at  Hesperia,  Cali- 
fornia, where  brevifolia  is  very  abundant,  I  was  fortunate 
enough  to  observe  many  of  the  moths  at  work  in  somewhat 
more  open  flowers,  where  their  operations  could  be  observed 
in  detail  by  the  use  of  a  bull's-eye  lantern,  to  which  they 
show  about  the  same  tolerance  as  the  other  species. 

When  about  to  deposit  an  egg,  having  selected  a  suitable 
flower,  the  female  of  synthetica  runs  to  the  bottom  of  the 
stamens  much  as  yuccasella  does,  makes  a  rapid  more  or 
less  complete  circuit  of  their  bases,  and  then  quickly  as- 
cends to  the  very  top  of  the  pistil,  her  thorax  rather 
higher  than  the  end  of  the  stigma,  and  with  her  short  but 
strong  ovipositor  cuts  through  the  thin  wall,  into  the  stylar 
channel,  rarely  as  much  as  2  mm.  below  the  tip  of  the 
stigma,  meantime  holding  fast  to  the  pistil,  the  stamens 
being  below  her  reach.  The  long  extensile  oviduct  is  then 
passed  through  the  puncture,  the  egg  being  laid  apparently 
within  the  ovarian  cell,  along  the  funicular  end  of  the 
ovules.  In  removing  the  oviduct  the  moth  not  infrequently 
carries  her  body  across  the  stigma,  so  that  at  first  sight  she 
appears  to  be  withdrawing  it  directly  from  the  mouth  of 
the  stylar  canal ;  but  I  have  never  seen  her  make  direct  use 
of  this  canal.  The  operation  consumes  more  time  than 
does  the  oviposition  of  either  yuccasella  or  maculata  as  I 
have  observed  them,  and  usually  takes  altogether  from  two- 
and-a-half  to  three  minutes.  Sometimes  two  or  more  eggs 
are  laid  before  the  stigma  is  pollinated,  but  commonly  after 
laying  each  egg  the  moth  retreats  to  the  bottom  of  the 
flower  and  then  again  ascends  the  pistil  until  her  head  is 
brought  even  with  the  stigma,  when  she  uncoils  the  large 
tentacles  from  their  resting-place  against  her  load  of  pollen 
and  passes  them  back  and  forth  in  the  stigmatic  chamber, 
with  almost  the  same  motion  as  the  eastern  species,  usually 
making  use  of  one  of  the  stigmatic  notches.  While  so 
employed  she  carries  the  rather  short  tongue  almost  straight 
out  above  the  stigma,  but  I  have  never  seen  her  make  any 
use  of  it  to  force  pollen  into  the  latter,  nor  has  she  beea 


FURTHER    STUDIES    OF    YUCCAS.  199 

observed  to  attempt  to  feed  on  the  slight  stigmatic  secre- 
tion nor  to  search  for  food  at  the  base  of  the  flower,  where, 
if  anywhere,  the  nectar  of  the  septal  glands  should  be 
found. 

In  this  Yucca,  the  short  spreading  pedicels  do  not  become 
erect  after  the  fertilization  of  the  flowers,  as  is  the  case 
in  the  capsular  species,  nor  do  they  become  markedly 
pendent  as  in  gloriosa  and  all  of  the  baccate  species,  but 
they  maintain  their  original  direction  during  the  ripening 
of  the  fruit.  As  in  all  of  the  Yuccas,  the  maturing  fruit 
develops  a  rather  firm  but  thin  core-like  endocarp  imme- 
diately surrounding  the  seeds,  but  in  this  species  the  thick 
exocarp,  instead  of  becoming  pulpy  as  in  the  baccate  spe- 
cies, or  hard  as  in  the  dehiscent  capsular  section,  assumes  a 
spongy  texture.  The  ripe  fruit,  readily  breaking  from  the 
tree,  consequently  possesses  large  bulk  and  low  specific 
gravity. 

Y.  GLORIOSA,  L.  —  Professor  Kiley*  states  that  this 
species,  which  occurs  in  the  aloifolia  region  of  the  south- 
east, is  pollinated  by  Pronuba  yuccasella  when  it  chances 
to  bloom  in  the  season  of  the  moth,  which  appears 
when  the  earlier  forms  of  Y.filamentosa  are  in  flower;  but 
its  blooming  is  more  commonly  later,  often  autumnal,  so 
that  it  less  frequently  produces  fruit  than  aloifolia,  and 
Dr.  Mellichamp  writes  me  that  although  he  has  seen  many 
blooming  plants  he  never  has  seen  fruit  of  gloriosa  but 
once,  and  that  was  from  a  summer  inflorescence.  Like 
aloifolia,  the  present  species,  in  some  of  its  rather  numer- 
ous forms,  is  said  to  fruit  occasionally  when  Pronuba  does 
not  occur  to  pollinate  it.f  Engelmann  has  shown,  how- 

*  l.  c.  lie,  117. 

t  Ellacombe,  in  the  Gardeners'  Chronicle  for  1880,  xiii.  p.  21,  reports 
that  in  England  he  has  more  than  once  had  well  formed  fruit  on  T,  re- 
curvifolia,  but  the  seeds  did  not  come  to  maturity ;  and  in  the  same 
journal  for  1885,  xxiv.  p.  628,  he  mentions  what  appears  to  be  the  same 
form,  under  the  name  of  T.  recurva,  as  having  fruited  in  1876,  some  of 
the  fruits  and  seeds  having  been  sent  to  Kew  and  to  Dr.  Engelmann,  a 
few  abortive  fruits,  which  soon  fell  off,  having  also  appeared  in  1885.  On 


200  MISSOURI    BOTANICAL    GARDEN. 

ever,  that  forms  of  aloifoHa  have  been  cultivated  frequently 
under  the  name  of  gloriosa  or  wrongly  referred  to  that 
species,*  and  an  editorial  mention  in  the  American  Agri- 
culturist for  1872,  xxxi.  p.  461,  of  the  apparent  absence 
of  insects  from  the  pulpy  fruits  ' '  as  soft  as  a  banana ' ' 
of  gloriosa,  in  Georgia,  undoubtedly  refers  to  aloifolia. 
Professor  Riley  limits  the  power  of  self-fertilization  so 
far  as  known  to  aloifolia  ;f  and  it  may  be  questioned 
whether  the  French  gloriosa  seedlings  mentioned  by  him 
in  a  quotation  from  The  Garden^  were  not  really  aloifolia, 
though  it  is  not  distinctly  stated  that  they  were  not  the 
result  of  artificial  pollination.  I  have  no  personal  knowl- 
edge of  the  fruiting  of  true  gloriosa  except  in  the  case 
figured  on  plate  7  of  the  Third  Garden  Report,  where  a 
specimen 'cultivated  in  Washington  produced  fruit  side  by 
side  with  a.  plant  of  aloifolia,  and  in  this  case  the  fruits 
were  more  or  less  deformed,  as  if  by  Pronuba. 

A  rather  narrow-leaved  form  of  this  species,  cultivated 
in  the  Garden  under  the  name  of  Y.  nivea,  bloomed  in 
the  early  part  of  September,  1892,  and  showed  nearly  as 
great  activity  of  the  septal  glands  as  the  specimen  of 
Guatemalensis  already  described,  the  nectar  appearing  in 
considerable  drops  within  the  bottom  of  the  perianth,  about 
the  almost  pilose  bases  of  the  filaments.  While  the  aloifo- 
lia of  the  Garden  was  fruitful  without  the  aid  of  Pronuba 
or  hand  pollination,  and  both  aloifolia  and  Guatemalensis 
yielded  fruit  when  artificially  pollinated,  this  plant  set 
no  fruit,  though  a  number  of  flowers  were  pollinated  by 
Mr.  Webber.  It  will  be  of  interest,  therefore,  to  have 
observations  made  on  gloriosa,  whether  wild  or  cultivated 
in  its  native  region.  The  later  blooming  of  this  species, 

the  other  hand  in  a  popular  account  of  Yucca  pollination,  in  his  Pflan- 
zenleben,  ii.  155,  Kerner  von  Marilaun  states  that  the  fruit  of  this 
species  is  quite  unknown  both  on  wild  and  cultivated  plants,  and  it 
is  said  that  the  moth  adapted  to  gloriosa  has  become  extinct. 

*  Trans.  St.  Louis  Academy,  iii.  211 ;  Collected  Writings,  297-8. 

t  Proc.  Amer.  Assoc.  Adv.  Sci.  xxxi.  467. 

I  Proc.  Amer.  Ass.  Adv.  Sci.  xxix.  624. 


FURTHER   STUDIES    OF   YUCCAS.  201 

like  that  of  certain  forms  of  filamentosa,  involving,  as  it 
appears  to  do,  a  loss  of  the  services  of  Pronuba  and  conse- 
quent sterility  in  all  but  exceptional  cases  of  early  blooming, 
is  especially  worthy  of  study,  considering  the  usual  close 
correspondence  of  the  period  of  blooming  of  the  Yuccas 
with  that  of  the  appearance  in  the  perfect  form  of  their 
Pronubas. 
c.  CELENOYUCCA,  with  dry ',  septicidally  dehiscent  capsules. 

Y.  RUPICOLA,  Scheele.  —  No  observations  have  been  re- 
corded on  the  pollination  of  this  Texan  species,  which 
Professor  Eiley*  believes  may  have  a  distinct  Pronuba.  It 
is  not  uncommon  from  Fort  Worth  southward,  on  the 
black  soil  with  intermingled  limestone,  but  I  failed  to  study 
wild  plants.  At  Dallas,  however,  through  the  kindness  of 
Mr.  J.  Reverchon,  I  was  able  to  examine  specimens  culti- 
vated on  his  place,  which  were  blooming  simultaneously 
with  the  wild  Y.  glauca,  var.  stricta  and  frequented 
by  Pronuba  yuccasella  like  the  latter.  These  plants  are 
abundantly  fertile  (each  crown  dying  after  blooming),  and 
the  structure  of  the  flower  indicates  that  the  moth  works 
on  them  as  she  does  on  the  filamentosa  group,  though  I 
was  unable  to  observe  her  actions.  Their  seedlings  are 
now  spontaneous  about  the  place,  and  so  variable  that  Mr. 
Reverchon  suspects  hybridization  with  the  native  variety  of 
glauca,  as  well  as  cultivated  forms  of  filamentosa.  This 
will  prove  an  interesting  subject  for  future  study,  since  the 
habits  of  Pronuba  in  caring  for  her  young  are  so  highly 
specialized,  and  the  details  are  so  minutely  carried  out,  that 
it  was  hardly  to  be  expected  that  a  given  individual  would 
indiscriminately  pass  from  one  species  of  Yucca  to  another, 
though  on  the  other  hand,  it  is  known  that  the  more  eastern 
species  are  all  pollinated  by  representatives  of  the  single 
species  of  Pronuba. 

Y.  ELATA,  Engelm.  (PL  10, 15,  22).—  Beginning  in  west- 
ern Texas,  about  the  limits  of  glauca,  this  Yucca  gradually 

*  L  c.  122. 


202  MISSOURI    BOTANICAL    GARDEN. 

increases  in  size  as  one  passes  into  Arizona,  where  it 
becomes  a  rather  large  tree,  but  of  far  simpler  habit  than 
brevifotta,  and  much  smaller  than  the  larger  plants  of  that 
species.  Its  underground  axis  is  of  the  glauca  type,  — 
long,  tough  and  branched,* — so  that  it  is  difficult  to  remove 
even  the  very  small  plants  from  the  ground.  The  inflo- 
rescence appears  to  be  terminal,  so  that  the  crown  which 
has  bloomed  has  its  apical  growth  destroyed ;  but  a  lateral 
bud  develops  into  a  new  crown,  and  in  time  a  number  of 
thick  new  heads  may  form  in  this  manner,  making  a  pluri- 
capitate  plant.  The  shortness  of  these  branches,  and  their 
dense  covering  of  long  spreading  leaves,  contrasted  with 
the  frequent  slendernesss  of  the  trunk,  after  its  lower  leaves 
have  become  reflexed  and  dry,  gives  the  tree  a  peculiar  and 
not  ungraceful  appearance,  quite  different  from  that  of 
any  other  species  native  of  the  United  States.  The  old 
flower  stalks,  when  above  the  reach  of  cattle,  usually  hold 
their  dehiscent  capsules  for  at  least  a  year,  and  at  length 
break  away  without  disarticulation  above  the  base,  which 
persists  for  years  along  the  side  of  the  stem,  closely  applied 
to  it  because  of  the  erect  sympodial  habit  of  the  latter. 

At  Eagle  Flat,  Texas,  I  was  able  to  spend  several  even- 
ings about  the  first  of  June  in  studying  the  pollination  of 
this  species,  which  there  rarely  becomes  six  feet  high  and 
begins  to  bloom  when  not  more  than  two  feet  high,  so  that 
observations  are  more  readily  made  than  on  the  taller 
plants  of  southern  Arizona. 

The  flowers  are  nearly  pure  white,  with  quite  acute  thin 
petals,  and  conform  in  most  respects  to  those  of  glauca. 
The  style,  however,  is  white,  as  in  nipicola  and  filamen- 
losa,  and  its  segments  are  little  thickened  dorsally.  The 
septal  nectar  glands  are  very  well  developed,  as  in  all  of 
this  group,  and  reach  to  the  base  of  the  ovary.  They  ap- 
pear to  be  slightly  more  active  than  in  related  species,  for 
a  little  nectar  was  recognized  in  several  flowers,  and  two 


Engelmann,  Coll.  Writings,  279,  280. 


FURTHER   STUDIES    OF   YUCCAS.  203 

species  of  small  bees*  were  taken,  probing  the  outlets  of 
the  conducting  grooves  at  the  base  of  the  pistil ;  but  these 
insects  were  not  seen  to  visit  the  stigma,  so  that  they 
play  no  part  in  pollination.  Considerable  numbers  of  a 
moth,  which  Professor  Kiley  determines  for  me  as  Acontia 
Arizona,  Hy.  Edw.,  were  seen  resting  in  the  flowers  during 
the  day,  and  settled  about  them,  especially  on  the  pedicels 
near  the  base  of  the  perianth,  at  night,  but  I  was  not 
fortunate  enough  to  determine  the  occasion  of  their  visits 
to  the  plant,  though  I  suspected  that  their  larvae  might 
develop  on  it.  So  far  as  can  be  seen,  they  play  absolutely 
no  part  in  its  pollination,  though  it  may  be  that  they  feed  to 
a  greater  or  less  extent  on  the  nectar.  The  stamens  shed 
their  pollen  promptly  on  the  opening  of  the  flowers,  and 
this  is  devoured  by  various  small  flies  with  the  same  avidity 
as  in  glauca,  and  with  about  the  same  prospect  of  effecting 
occasional  casual  pollination  as  in  that  species. t 

Like  the  eastern  Yuccas,  elata  is  pollinated  by  Pronuba 
yuccasella,  the  work  of  which  was  repeatedly  observed  in. 
detail  at  Eagle  Flat,  where  the  moths  were  abundant. 
During  the  day,  like  the  Eastern  moths  and  those  of  baccata, 
they  rest  in  the  flowers  with  their  heads  directed  to  the  base 
of  the  petals.  Shortly  before  sunset  many  of  them  be- 
come active  (as  is  the  case  on  filameniosa  at  St.  Louis), 
the  females  beginning  their  work  of  oviposition  and  pol- 
lination, while  the  males  run  and  fly  actively  from  flower 
to  flower  in  search  of  their  mates ;  and  this  is  continued 
through  the  greater  part  of  the  night. 

When  about  to  deposit  an  egg,  the  moth  here,  as  on 
jilamentosa,  runs  nervously  about  within  the  bottom  of  the 
flower,  then  scrambles  to  the  top  of  the  pistil  and  backs 
down  between  two  stamens  by  a  succession  of  jerks  until 
her  head  is  about  level  with  the  base  of  the  style.  Hold- 
ing to  the  pistil  by  the  pro-  and  meso-thoracic  legs,  the  last 


*  Determined  by  Mr.  Charles  Robertson  as  Agapostemon  Texanus, 
and  Halictus  albipennis,  9 . 
f  See  a  note  by  the  writer  in  Riley,  i.  c.  126. 


204  MISSOURI    BOTANICAL    GARDEN. 

pair  not  infrequently  carried  out  over  the  filaments,  she 
then  punctures  the  ovary  and  the  egg  is  consigned  to  its 
place  in  the  manner  so  well  described  by  Riley  for  fila- 
mentosa ;  but  as  a  rule  the  operation  appears  to  consume 
rather  less  time  on  data  than  on  the  other  Yuccas  I  have 
studied.  Usually  each  oviposition  is  followed  by  pollination, 
in  which,  so  far  as  I  can  see,  the  moth  acts  precisely  as  on 
filamentosa  ;  but  in  a  few  cases  two  eggs  were  laid  before 
pollen  was  carried  to  the  stigma,  and  under  the  bright  light 
of  the  lantern  the  actions  of  the  moth  are  sometimes  so 
disturbed  that  she  will  leave  a  flower  after  ovipositing,  with- 
out subsequently  pollinating  it.  I  have  also  observed  on 
this  species  that  she  sometimes  interrupts  the  act  of  polli- 
nation to  coil  the  tentacles  against  her  load  of  pollen,  after 
which  they  are  again  inserted  in  the  stigma,  thus  securing 
for  the  latter  a  larger  amount  of  pollen ;  but  I  have  no 
doubt  this  procedure  is  as  common  on  the  other  species  pol- 
linated by  yuccasdla.  In  one  instance,  a  moth  disturbed 
by  the  light  while  ovipositing  left  the  flower  without  polli- 
nating it,  but  her  first  act  on  going  into  another  flower  was 
to  thrust  her  pollen-laden  tentacles  into  the  stigma,  though 
it  appears  to  be  unusual  for  this  to  precede  oviposition. 

The  collection  of  pollen  from  the  anthers  was  not  closely 
observed  on  elata,  but  on  several  occasions  the  moth,  when 
disturbed  in  oviposition,  ran  upon  a  stamen,  shaking  it  quite 
violently  and  making  several  passes  at  the  anther  with  her 
tentacles,  as  if  impelled  by  fright  to  discontinue  one  of  her 
customary  occupations  only  to  engage  in  another, —  though 
her  motions  were  too  quick  and  nervous  for  me  to  see  that 
she  actually  gathered  any  pollen.  There  is,  however,  no 
reason  to  doubt  that  the  collection  of  pollen  is  similar  to 
that  on  Jilamentosa,  where,  however,  it  is  by  no  means 
always  slow  and  easy  of  detailed  observation. 

When  I  passed  over  the  Texas  and  Pacific  road  again, 
about  a  month  later,  a  fair  crop  of  partly  grown  fruits  was 
seen,  the  usual  constriction  or  indentation  being  noticeable 
over  the  Pronuba  punctures.  At  Benson,  in  southern 


FURTHER   STUDIES    OF   YUCCAS.  205 

Arizona,  where  elata  assumes  much  larger  proportions, 
though  it  bloomed  very  freely  this  year,  I  did  not  suc- 
ceed in  finding  any  of  the  moths  in  a  day-light  search  in 
the  early  part  of  June,  just  as  the  species  was  coming  into 
bloom,  nor  were  many  ripening  capsules  to  be  found  when 
I  again  visited  this  locality  toward  the  end  of  the  month. 
But  the  few  fruits  which  had  set  showed  the  usual  Pro- 
nuba  deformity,  and  a  considerable  number  of  last  year's 
capsules  were  found,  all  containing  the  remains  of  tunneled 
seeds,  and  perforated  by  the  escaped  larvae. 

Y.  GLAUCA,  Fraser,  Cat.  1813,  not  Sims.  (  Y.  angusti- 
folia,  Pursh,  1814,  and  most  recent  writers).* —  It  has  long 
been  known  that  the  pollinator  of  this  representative  Rocky 
Mountain  species  is  JPronuba  yuccasella,  which  appears 
coetaneously  with  its  flowers  in  the  west  and  southwest, 
but,  being  more  closely  connected  in  the  east  with  the  later- 
blooming  filamentosa,  only  exceptionally  appears  early 
enough  to  pollinate  even  the  latest  blooming  flowers  of 
glauca  on  plants  cultivated  in  Washington  and  St.  Louis  f 
(where  a  few  capsules  were  again  matured  in  the  sum- 
mer of  1891).  The  only  observations  on  the  behavior  of 
the  moth  on  wild  plants  that  I  know  of  are  those  reported 
by  the  writer  in  1891  from  the  vicinity  of  Manitou,  Col.| 
Incomplete  as  these  are,  they  show  that  her  actions  are 
quite  the  same  as  on  filamentosa.$ 


*  Though  for  reasons  of  expediency  it  would  be  better  to  preserve  for 
this  plant  the  name  of  angustifolia,  under  which  it  is  universally  known, 
the  short  description  in  Eraser's  Catalogue  is  sufficiently  characteristic,  in 
connection  with  the  northern  locality  from  which  his  specimens  were 
obtained,  to  make  it  necessary  to  restore  his  name.  The  later  Y.  glauca, 
Sims,  is  an  entire-leaved  plant  which  I  should  refer  to  jilamentosa. 

t  Riley,  I.  c.  116,  121,  128.  J  See  Riley,  L  c.  124. 

§  The  principal  references  under  this  species  are  as  follows :  Bruner, 
Entomol.  Bull.  U.  S.  Dept.  Agriculture,  ii.  9.  Meehan,  Bull.  Tor- 
rey  Bot.  Club,  iv.  63;  Proc.  Phila.  Acad.  1873,  414;  Proc.  Ainer.  Ass. 
Adv.  Sci.  xxx.  205;  Amer.  Nat.  1881,  807;  Proc.  Phila.  Acad.  1888,  275, 
general  abstracts  in  Proc.  Amer.  Ass.  xxxvii.  284  and  Bot.  Gaz.  1888, 
237.  Eiley,  Trans.  St.  Louis  Acad.  iii.  570;  Mo.  Ent.  Kept.  v.  159;  Insect 
Life,  i.  363 ;  Kept.  Mo.  Bot.  Gard.  iii.  various  places. 


206  MISSOURI   BOTANICAL    GARDEN. 

The  typical  Yucca  glauca,  as  represented  in  Colorado 
and  Kansas,  spreads  below  ground  by  a  series  of  rather 
slender  but  very  strong  axes,  and  in  its  more  highly 
developed  form  has  a  more  or  less  developed  mostly  pros- 
trate stoutish  trunk  above  ground.  So  far  as  I  know, 
whether  caulescent  or  acaulescent,  a  given  axis  usually 
blooms  repeatedly. 

Y.  GLAUCA,  var.  STRICTA,  (Sims.).  (Y.  angustifolia, 
var.  mollis,  Engelm.)  (PI.  22). —  In  its  broader  flaccid 
leaves,  occasionally  an  inch  wide,  this  forms  an  approach 
from  glauca  to  the  Eastern  filamentosa,  but  its  range,  — 
Arkansas,  Louisiana  and  Texas, —  brings  it  strictly  within 
the  region  of  the  former  and  its  immediate  allies.  Unlike 
the  more  representative  glauca,  however,  a  given  crown 
seems  more  likely  to  fruit  but  once,  though  the  subterran- 
ean parts  are  similar  in  both.  Its  delicate  greenish-white 
flowers,  most  commonly  in  a  simple  raceme,  possess  the 
general  characters  of  those  of  the  type,  and  are  slightly 
fragrant.  The  styles,  though  somewhat  variable  in  color, 
are  commonly  bright  green  as  in  the  type,  so  that  they 
contrast  with  the  ovary,  which  is  colored  similarly  to  the 
perianth.  The  stylar  canal  is  open  and  in  evident  com- 
munication with,  the  cells  of  the  ovary,  and  at  times  con- 
tains a  plentiful  secretion.  No  nectar  was  observed  at 
Dallas,  Texas,  where  I  had  an  opportunity  of  examining 
the  flowers  in  several  localities,  but  the  septal  glands  are 
large  and  with  large  conducting  grooves,  as  is  generally  the 
case  in  the  filamentosa  group. 

Many  years  ago  Boll  *  made  a  number  of  observations 
about  Dallas  on  the  Yuccas,  some  of  which  were  doubtless 
of  this  variety.  While  he  did  not  at  first  discriminate  be- 
tween Pronuba  and  the  related  Prodoxus  decipiens,  —  which 
Professor  Riley  has  well  called  the  Bogus  Yucca  Moth,  — 
and  especially  the  still  more  deceiving  Prodoxus  intermedium, 


*  Boll,   Stettin.  Entomolog.  Zeitung,  1876,  401,  quoted  by  Riley  i» 
Trans.  St.  Louis  Academy,  iii.  571. 


FURTHER  STUDIES  OF  YUCCAS.  £07 

and  fell  into  some  other  serious  errors,  he  appears  to  have 
been  the  first  to  observe  the  collection  of  pollen  by  the 
female  Pronuba,  though  not  with  the  detail  given  by  Pro- 
fessor Eiley  in  the  account  of  his  own  observation  of  this 
operation  on  Y .  Jilamentosa  .* 

The  pollinator  of  this  variety,  as  of  the  more  representa- 
tive form  of  the  species,  is  the  white  Pronuba  yuccasella. 
As  on  other  Yuccas,  the  moth  is  quite  sluggish  within  the 
flowers  during  the  day,  apparently  considering  itself  con- 
cealed by  its  protective  coloration.  Numerous  laden  females 
were  taken  and  observed  about  the  flowers  at  night,  and  copu- 
lation within  the  flower  was  several  times  seen  in  the  evening, 
but  I  was  unfortunately  not  able  to  see  these  moths  engaged 
in  either  pollination  or  oviposition.  The  pale  poll  en,  how- 
ever, is  very  evident  in  the  green  stigmas,  where  there  is  lit- 
tle reason  to  doubt  they  have  placed  it.  Egg  punctures  were 
also  observed  in  numbers,  in  such  a  situation  on  the  ovary  as 
to  show  that  the  moth  occupies  the  same  position  when  ovi- 
positing as  on  filamentosa.  On  the  older  panicles  a  fair 
percentage  of  fruit  was  maturing  at  the  time  of  my  exam- 
ination at  Dallas,  and  showed  the  usual  Pronuba  constric- 
tions, and  several  capsules  of  the  preceding  year  which  were 
found  had  been  perforated  by  escaping  larvae,  and  contained 
remnants  of  tunneled  seeds. 

At  Putnam,  Texas,  considerably  west  of  Dallas,  a  larger 
form  of  what  I  take  to  be  this  variety  of  glauca  occurs, 
with  narrower  leaves ;  and  about  the  end  of  May  this  was 
passing  out  of  bloom,  just  as  elata,  still  further  west,  was 
beginning  to  flower.  At  this  place,  fewer  capsules  had 
set  than  about  Dallas,  but  these  showed  the  irregularities 
indicative  of  oviposition  by  Pronuba,  which  had  quite  dis- 
appeared ;  and  some  of  the  stalks  of  the  preceding  year 
still  bore  capsules  which  were  marked  by  the  escape 
perforations  of  her  larvae. 


*  Proc.  Amer.  Assoc.  Adv.  Science,  1882,  xxxL  467-8;  Third  Garde* 
Report,  106,  pi.  38,  f.  2. 


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J.  ELIOT  COIT 
Please  return. 


208  MISSOURI    BOTANICAL   GARDEN. 

Y.  FILAMENTOSA,  L.  (PL  11,  22).  —  This  species  is  the 
subject  of  nearly  all  of  the  pollination  observations  hereto- 
fore published,  and  its  interrelations  with  Pronuba  yucca- 
sella  are  so  well  known  that  I  need  scarcely  do  more  than 
refer  to  Professor  Riley's  account  in  the  last  Garden  Re- 
port. In  St.  Louis  the  observations  of  preceding  years  * 
have  been  repeated  by  myself  and  others,  and  on  several 
occasions  the  collection  of  pollen  was  again  witnessed,  but 
in  the  same  imperfect  manner  as  last  year,  owing  to  the 
haste  of  the  moth.  Although  special  attention  has  been 
given  to  this  point  I  have  failed  to  see  the  moth  attempt 
to  feed  on  either  the  stigmatic  secretion  or  the  septal 
nectar,  nor  have  I  been  able  to  reconvince  myself  that  she 
makes  use  of  the  tongue  in  pollination,  as  I  once  thought. 
As  in  the  case  of  Yucca  elala,  the  moth,  when  disturbed 
by  the  lantern  while  ovipositing,  sometimes  attacks  the 
stamens,  as  if  intending  to  reinforce  her  load  of  pollen,  but 
in  most  cases  without  proceeding  far  in  this  before  retreat- 
ing to  the  resting  position  within  the  base  of  the  flower,  or 
leaving  the  latter.  In  addition  to  the  insects  heretofore 
seen  in  the  flowers  of  this  species,  I  have  this  year  seen 
several  specimens  of  a  rather  large  flower  beetle,  Trichius 
piger,  in  the  bottom  of  the  flowers,  with  their  heads  at  the 
outlet  of  the  nectar  grooves  as  if  feeding  on  the  small 
amount  of  secretion. 

HESPEROYUCCA. 

Filaments  aduate  to  the  petals  below :  po  lien  agglutinated  in  coherent 
masses:  style  slender:  stigma  capitate,  hyaline-papillate,  with  a  micro- 
scopic axile  canal:  fruit  capsular,  loculicidal. 

Y.  WHIPPLEI,  (Torr.)  Baker.  (PI.  16,  23).— From  the 
San  Bernardino  Mountains  north  to  the  latitude  of 
Monterey  and  south  into  Lower  California  in  the  Coast 
Range,  this  peculiar  species  is  very  abundant,  especially 


*  See  Eiley,  1.  c.  123  etc.  Ellacombe  in  the  Gardeners'  Chronicle 
for  1872,  p.  1457,  Morse,  ibid.  1885,  xxiv.  598,  and  Smith,  ibid.  1872,  1391, 
report  spontaneous  capsules  on  this  species  in  England.  This  should  be 
compared  with  the  references  given  under  gloriosa. 


FUKTHER    STUDIES    OF    YUCCAS.  209 

through  the  Tehachapi  region,  the  lower  mountains  being 
often  densely  covered  with  its  large  frequently  cylindrical 
panicles  or  old  fruit  stalks.  The  most  typical  form,  as  it  oc- 
curs in  the  Cajon,  Tehachapi,  and  San  Luis  Obispo  regions,  is 
almost  always  cespitosc,  sometimes  with  eight  or  ten  crowns 
clustered  over  a  single  root,  owing  to  the  formation  of 
lateral  branches  near  the  base  of  the  main  stem,  even  while 
this  is  quite  young.  After  blooming,  a  given  crown  dies, 
but  the  several  heads  of  these  cespitose  plants  may  pro- 
long the  life  of  the  plant  through  a  series  of  years,  until 
the  last  of  them  has  flowered.  The  leaves  of  this  f orni  are 
commonly,  though  not  always,  quite  rigid. 

The  flowers  are  as  variable  as  in  the  true  Yuccas,  ranging 
from  globose  to  bell-shaped,  and  there  are  great  individual 
differences  in  the  degree  to  which  they  expand,  but  they 
are  not  typically  rotate,  as  Dr.  Engelmann  was  led  to 
believe  by  some  photographs  looking  directly  into  rather 
widely  opened  flowers.  They  differ  from  those  of  other 
species  in  having  the  glabrous  (but  still  minutely  granu- 
lated) filaments  attached  to  the  lower  part  of  the  petals, — 
a  character  not  well  shown  in  the  figures  in  the  last  Report, 
so  that  as  they  open  the  stamens  are  drawn  away  from  the 
ovary  instead  of  lying  in  close  apposition  to  it.  The  small 
oval  anther  cells  are  commonly  tipped  by  a  bunch  of  white 
hairs,  though  in  specimens  observed  on  the  mountain  sides 
above  San  Luis  Obispo  these  were  reduced  to  one  or  two 
on  each  cell  or  were  apparently  entirely  wanting,  and  I  have 
no  idea  as  to  their  function.  On  dehiscing,  the  cells  con- 
tract in  such  a  manner  as  to  expose  the  pollen  freely,  but 
at  the  same  time  prevent  it  in  most  instances  from  falling 
out,  as  it  so  frequently  does  in  the  true  Yuccas.  As  Riley 
has  already  shown,*  the  pollen  of  this  plant  is  not  loose 
and  powdery,  as  in  Yucca  proper,  but  glutinous.  The  con- 
tents of  each  anther  cell,  in  fact,  form  a  rather  consistent 
two-lobed  moist  mass,  which  is  held  by  its  lower  part  but 
protrudes  prominently  from  the  open  anther. 


2j Q  MISSOURI    BOTANICAL    GARDEN. 

The  pistil  differs  materially  from  that  of  the  true  Yuccas 
in  having  the  ovary  free  from  those  longitudinal  depres- 
sions which  usually  correspond  with  the  appressed  stamens, 
and  in  possessing  a  short  contracted  style  surmounted  by  a 
capitate  stigma,  green  toward  the  center,  where  it  appears 
slightly  indented,  and  covered  with  very  long  hyaline  deli- 
cate papillae  which  are  always  moist  with  abundant  secre- 
tion that  at  length  becomes  almost  gelatinous  over  the 
middle  of  the  stigma.  From  the  central  depression  of 
the  stigma,  a  fine  but  unobstructed  canal  passes  down 
the  style  and  communicates  with  the  top  of  the  cells 
of  the  ovary.  The  nectar  apparatus  is  well  developed,  the 
septal  glands,  though  narrow,  commonly  reaching  to  the 
base  of  the  ovary,  while  the  conducting  groove  is  of  cor- 
responding size.  My  observations  lead  to  the  conclusion 
that  the  glands,  though  smaller  than  in  the  filamentosa 
group,  are  more  active  than  in  other  species  studied  by  me, 
with  the  possible  exception  of  gloriosa  and  GuatemaleTisis, 
for  I  have  repeatedly 'seen  considerable  drops  of  nectar  at  the 
basal  outlets  of  the  grooves,  especially  in  the  early  morn- 
ing or  in  damp  foggy  weather  when  evaporation  was  slow, 
and  in  pendent  flowers  similar  drops  have  been  seen  several 
times  over  the  grooves  at  either  the  middle  or  top  of  the 
ovary,  along  the  smooth  surface  of  which  they  had  appar- 
ently rolled  from  the  outlets  of  the  conducting  grooves. 

Professor  Riley  has  shown  that  Whipplei  is  pollinated 
by  a  distinct  Pronuba,  which  he  names  P.  maculata,  of  a 
white  general  color,  but  somewhat  variously  mottled  with 
black,  especially  towards  the  ends  of  the  wings.*  He 
records  the  occurrence  of  the  moth  in  the  vicinity  of  San 
Diego,  Los  Angeles,  Newhall,  and  Caliente.  I  have  also 
taken  specimens  at  Summit  in  the  Cajon  Pass,  at  Saugus, 
San  Luis  Obispo,  and  along  the  Santa  Ynez  river  above 
Santa  Barbara,  besides  seeing  evidence  of  its  work  in  the 

*  I.  c.  121,  139;  Insect  Life,  iv.  370,  note.  For  other  notes  by  the 
same  author,  see  Proc.  Ent.  Soc.  Washington,  1888,  i,  154,  and  Insect 
Life,  i.  372. 


FURTHER    STUDIES   OF   YUCCAS.  211 

old  fruits  both  at  Newhall  and  Caliente.  The  only  other 
insects  observed  by  me  in  the  flowers,  were  small  flies  and 
beetles  similar  to  those  so  frequently  seen  in  the  flowers  of 
the  Yuccas,  a  few  small  bees,  and  on  one  occasion,  hive 
bees.  The  latter  were  primarily  attracted  by  an  abundant 
watery  fluid  on  the  outside  of  the  flowers,  of  undiscovered 
origin,*  and  entered  the  flowers  only  incidentally.  The 
others  gathered  nectar  from  the  base  of  the  corolla,  where 
the  nectar  grooves  open.  Neither  were  seen  to  touch  either 
the  anthers  or  stigma,  and  it  is  doubtful  if  they  carry  pollen 
from  one  to  the  other,  even  by  accident,  which  is  the  only 
way  in  which  this  could  happen. 

From  its  pronounced  fragrance,  which  while  it  is  of  the 
general  yucca  type  somewhat  recalls  that  of  the  tuberose, 
its  active  nectar  glands,  pollen  aggregated  into  crude 
pollinia,  and  large  capitate  stigma  covered  with  long  moist 
papillae,  Whipplei  would  appear  quite  likely  to  be  pol- 
linated by  visitors  other  than  Pronuba ;  and,  as  Professor 
Riley  has  well  said,  of  all  the  Yuccas  it  would  seem  to  be 
most  easily  self-fertilizable.  In  fact,  in  the  lower  part  of 
the  Cajon  Pass  when  the  species  was  in  the  best  of  its 
blooming  period,  very  few  Pronubas  were  seen ;  and,  while 
there  was  a  corresponding  scarcity  of  setting  fruit,  a  few 
plants  were  found  with  more  or  less  abundant,  partly 
developed  but  unusually  diminutive  capsules  in  which  no 
oviposition  scars  could  be  detected,  and  some  of  the  fruit 
of  the  preceding  year  was  of  the  same  dwarf  character  and 
without  either  escape  holes  or  the  masses  of  tunneled  seeds 
almost  invariably  seen  in  old  capsules  elsewhere.  Frequent 
observation  has  shown  that  the  pollinia  may  be  deposited 
on  the  margin  of  the  stigma  directly  from  the  anthers  in 
closing  flowers,  particularly  the  small  ones  to  which  these 
dwarf  capsules  correspond ;  and  it  was,  therefore,  with  no 
little  surprise  that  I  noted,  in  contrast  with  this  apparent 
power  of  self-fertilization,  that  with  this  single  exception,  no 

*  See  note  under  baccata  for  the  occurrence  of  a  similar  exudation  i» 
species  of  Yucca  proper. 


212 


MISSOURI    BOTANICAL    GAHDEX. 


fruit  whatever  was  found  except  that  which  clearly  showed 
the  work  of  Pronuba.  At  best,  therefore,  I  should  say  that 
where  its  proper  Pronuba  is  absent,  WJilpplei  has  only  the 
limited  power  of  self-pollination,  or  pollination  by  other 
agents,  that  is  possessed  by  aloifolia  among  the  true  Yuc- 
cas. I  have  also  no  evidence  that  pollen  tubes  ever  develop 
in  such  a  manner  as  to  reach  and  fertilize  the  ovules 
from  pollinia  placed  on  the  margin  of  the  stigma,  although 
search  was  made  for  something  of  the  sort;  and  a  deter- 
mination of  the  extent  to  which  fertilization  in  this  manner 
is  possible  must  be  made  by  a  series  of  experiments  such  as 
I  could  not  carry  out  in  the  time  at  my  disposal.* 

The  characters  of  Pronuba  maculata,  have  been  so  fully 
given  by  Eiley  that  nothing  need  be  added  to  his  descrip- 
tion. From  the  frequently  open  character  of  the  flowers, 
and,  especially,  the  withdrawal  of  the  stamens  from  the 
pistil,  these  moths  are,  however,  constrained  to  behave 
quite  differently  from  the  other  species  of  their  genus ;  and 
very  probably  in  connection  with  the  more  diurnal  nature 
of  the  Hesperoyucca  flowers,  they  are  far  more  active  in 
the  day  time  than  their  congeners  are.  Unless  locally  ab- 
sent, they  are  readily  observed  whenever  the  flowers  are 
examined,  either  resting  in  them  or  engaged  in  pollination 
or  oviposition,  and  at  first  sight  it  is  difficult  to  say  whether 
they  are  quiescent  or  engaged  in  the  latter  operation,  for, 
unlike  the  other  known  Pronubas,  they  rest  with  the  head 
toward  the  stigma,  usually  standing  upon  the  side  of  the 
ovary,  —  a  position  almost  identical  with  that  taken  in  ovi- 

*  Since  the  above  was  written,  Professor  Riley,  under  date  of  October 
13,  1892,  writes  me  that  in  a  manuscript  report  on  the  pollination  of 
Whipplet,  Mr.  Coquillet  of  Los  Angeles  records  the  seeding  this  year  of  a 
number  of  pods  or  panicles  which  he  had  covered  with  gauze  before  any  of 
the  flowers  opened.  Professor  Kerner  von  Marilaun  (Pflanzenleben,  ii. 
155,  figures  1  to  5),  states  that  in  repeated  cases  of  blooming  in  the 
Vienna  Garden  this  species  has  never  matured  its  fruit.  The  figures 
which  accompany  his  account  of  Yucca  pollination  represent  some  Eu- 
yucca,  — apparently  a  form  of  jilamentosa,  —  though  they  bear  the  name 
WMpplei;  and  the  moth  represented  as  pollinating  the  flower  (adapted  by 
the  artist  from  Riley's  figures),  is  yuccasella. 


FURTHER  STUDIES  OF  YUCCAS.  213 

positing.  While  in  this  attitude  they  are  very  observant, 
and  the  approach  of  one's  face,  even  at  a  distance,  causes 
them  to  retire  further  down  the  pistil.  When  so  disturbed 
they  are  also  very  apt  to  drop  suddenly  from  the  flower  and 
take  wing,  seeking  a  new  retreat. 

I  have  not  seen  the  collection  of  pollen  by  the  typical 
form  of  this  moth,  but,  from  the  way  in  which  the  load  is 
carried,  there  is  no  doubt  that  it  is  accumulated  in  the 
manner  presently  to  be  described  for  the  pollinator  of  what 
I  take  to  be  the  Yucca  graminifolia  of  Wood,  and  I  see 
no  reason  to  doubt  that  it  frequently  takes  place  in  the 
bright  daylight,  as  both  oviposition  and  pollination  do. 
Either  of  the  latter  operations  may  be  witnessed  at  any 
time  during  the  day,  if  the  flowers  are  not  approached 
too  suddenly. 

When  the  moth  is  about  to  deposit  an  egg,  she  usually 
moves  about  in  the  lower  part  of  the  flower  much  as  the 
other  species  do,  commonly  dragging  the  tip  of  the  ovi- 
positor along  the  parts  she  walks  on  as  if  wiping  off 
extruded  secretion,  but  also  seemingly  using  it  as  a  tactile 
organ  while  she  assumes  the  position  best  suited  to  ovi- 
position, which  is  nearly  the  same  as  that  taken  while  at 
rest.  Standing  on  the  side  of  the  pistil,  she  then  bends  the 
abdomen  sharply  forward  so  as  to  bring  the  ovipositor 
to  about  the  middle  of  the  ovary,  which  she  pierces  at 
the  thinnest  part,  namely,  about  1  mm.  from  the  septal 
groove.  As  a  general  thing  not  more  than  six  eggs  are 
laid  in  a  given  pistil, —  one  on  either  side  of  each  septum, — 
and  frequently  the  number  is  smaller  than  this,  so  that 
even  if  they  all  hatch,  which  is  not  likely  to  be  the  case, 
there  is  rarely  more  than  one  larva  to  each  tier  of  seeds, 
and  consequently  a  fair  percentage  of  the  seeds  are  allowed 
to  come  to  maturity .  In  the  very  succulent  white  ovary 
the  puncture  made  in  laying  an  egg  is  usually  seen  easily 
immediately  after  the  ovipositor  is  withdrawn,  and  a  rather 
large  drop  of  clear  sap  not  infrequently  exudes  from  it 
within  a  short  time. 


214  MISSOURI    BOTANICAL   GARDEN. 

Having  withdrawn  the  oviduct,  in  doing  which  she  moves 
up  so  that  her  head  is  about  level  with  the  stigma,  or  even 
before  this  organ  is  entirely  freed,  the  moth  usually  pro- 
ceeds to  pollination ;  but  it  is  not  infrequent  for  two  eggs 
to  be  laid  between  each  two  visits  to  the  stigma,  and,  owing 
to  her  peculiar  alertness,  she  appears  to  be  even  more  easily 
frightened  into  omitting  pollination  than  are  the  other 
species  of  Pronuba.  Standing  with  her  head  at  about  the 
height  of  the  stigma,  with  the  short  tongue  projecting  out 
in  front,  she  uncoils  her  long  tentacles  from  the  compact 
mass  of  pollinia,  —  which  she  carries  similarly  to  the 
other  Pronubas,  —  only  that  small  part  of  her  burden  which 
adheres  to  the  bases  of  the  tentacles  being  removed  from  it, 
and,  raising  her  body  on  tiptoe,  she  very  slowly  saws  the 
tentacles  back  and  forth  across  the  top  of  the  stigma,  gen- 
erally following  one  of  the  three  shallow  grooves,  and  very 
carefully  working  their  slender  tips  into  the  more  or  less 
gummy  exudation  over  the  central  depression.  Sometimes 
the  operation  is  interrupted  long  enough  to  admit  of  the 
tentacles  being  coiled  back  against  the  load  of  pollen  and 
again  extended ;  but  the  curious  manner  in  which  her  head 
is  held  back  from  the  stigma  as  a  rule  prevents  any  of  the 
main  load  from  reaching  even  the  marginal  papillae. 

On  first  witnessing  this  operation,  I  was  impressed  by 
the  much  slower  motion  of  the  moth  than  usual,  and  the 
evident  care  which  she  took  to  run  the  ends  of  the  tentacles 
into  the  central  depression  of  the  stigma,  which  I  then  sup- 
posed to  be  solid ;  the  subsequent  discovery  of  the  stylar 
canal,  communicating  with  the  ovarian  cells,  showed  that 
it  is  into  this  narrow  passage  that  she  so  carefully  guides 
the  tips  of  her  tentacles  with  their  modicum  of  pollen,  and 
no  doubt  the  abundant  stigmatic  secretion  serves  not  only 
to  foster  the  development  of  the  nascent  pollen  tubes  after 
pollination,  but,  wetting  the  tentacles,  aids  in  the  disinte- 
gration of  her  mass  of  pollinia.  These,  if  really  related  to 
her  work,  would  seem  to  have  acquired  their  coherent 
structure  as  a  means  of  facilitating  their  collection,  rather 


FURTHER   STUDIES    OF   YUCCAS.  215 

than  as  an  adaptation  to  their  removal  bodily  from  the 
anther  to  the  stigma  as  is  the  case  in  orchids  and  asclepiads, 
where,  however,  special  means  of  secure  attachment  to  the 
insect  accompany  this  aggregation  of  the  pollen  grains  into 
a  large  mass. 

As  in  the  other  capsular  Yuccas,  the  pedicel  of  the  fer- 
tilized flower  soon  becomes  erect,  and  the  ovary  shortly 
begins  to  enlarge  and  assumes  a  bright  green  color.  Owing 
to  the  injury  inflicted  in  piercing  its  wall,  the  part  immedi- 
ately about  the  puncture  does  not  take  a  very  active  part 
in  this  growth,  and  a  cross  section  here  shows  a  decided 
difference  in  size  between  the  punctured  and  unpunctured 
half  cells  of  the  ovary,  and,  as  the  enlargement  of  the 
capsule  continues,  a  decided  pit  appears,  mostly  of  a  darker 
green  than  the  surrounding  parts. 

H.  WHIPPLEI,  var.  GRAMINIFOLIA,  (Wood).  (PI.  13,  23). — 
What  I  take  to  be  this  form,  is  the  common  Spanish  Bayo- 
net of  San  Bernardino,  beginning  near  the  foot-hills  north 
of  the  city  and  extending  up  the  smaller  canons  and  upon 
the  mountain  sides  to  an  elevation  of  1000  feet  or  more, 
and,  in  the  Cajon  Pass,  reaching  up  toward  Cajon  Station, 
where  the  steep  ascent  of  the  pass  begins.  Recent  notes 
from  Dr.  Yates,  of  Santa  Barbara,  show  that  a  plant  of 
the  general  character  of  this  variety  occurs  in  the  mount- 
ains above  that  city,  in  addition  to  the  typical  Whipplei; 
and  it  appears  to  pass  eastwards  from  the  San  Bernardino 
region,  though  I  am  not  in  possession  of  detailed  informa- 
tion as  to  its  distribution  outside  of  the  limited  area  between 
San  Bernardino  and  the  foot-hills  north  of  that  city.  The 
plants  are  very  abundant  around  the  Arrowhead  Springs, 
where  the  type  of  Whipplei  does  not  occur,  and  I  was 
able  to  make  a  rather  careful  study  of  them  there  shortly 
after  the  middle  of  April,  when  they  were  just  coming  into 
bloom,  as  well  as  a  month  later,  when  their  flowering  period 
was  nearly  past;  and,  still  later,  in  company  with  Mr.  S. 
B.  Parish,  I  had  an  opportunity  to  drive  over  the  principal 
part  of  the  valley  covered  by  this  form,  at  a  time  when  its 


216 


MISSOURI   BOTANICAL    GARDEN. 


pollinator  had  almost  completely  disappeared,  though  some 
spikes  were  yet  blooming. 

In  aspect,  this  variety  differs  from  the  typical  Whipplei  of 
the  mountains  in  not  being  cespitose,  and  in  its  thinner,quite 
flexible,  often  broader  and  longer  leaves.  Its  flowers  are 
similar  to  those  of  the  type  except  that  they  are  commonly 
more  or  less  brown-purple,  and  they  are  as  variable  in 
form.  All  about  Arrowhead,  at  the  time  of  my  first  visit, 
there  were  evidences  of  the  work  of  a  Fronuba  in  last 
year's  capsules,  which  were  very  abundant,  and  I  conse- 
quently expected  to  be  able  to  study  the  work  of  P.  macu- 
lata  in  the  opening  panicles.  I  was,  however,  surprised  to 
see  that  the  only  Pronuba  found  on  the  plants  of  this 
vicinity,  though  possessing  the  usual  maculata  structure, 
was  of  a  beautiful  jet  black  color,  and,  with  the  exception 
of  a  single  specimen,  in  which  the  thorax  was  dingy  white, 
this  proved  to  be  the  case  with  the  thousands  of  moths 
seen  or  captured  about  Arrowhead  and  in  the  valley  to  a 
point  near  Irvington.  I  have  called  this  rnelanic  form  P. 
maculata,  var.  aterrima.* 

The  females  of  this  black  Pronuba  rest  upon  the  ovary 
with  their  heads  toward  the  stigma,  precisely  like  the  typi- 
cal maculata,  while  the  males  also  commonly  stand  upon 
the  petals.  Like  the  maculate  moths,  they  are  very  alert, 
and  quite  ready  to  drop  from  the  flower  and  take  wing 
when  disturbed.  They  are  also  active  during  the  day,  the 
males,  especially,  running  and  flying  from  flower  to  flower 
in  quest  of  their  mates ;  and  copulation  is  seen  within  the 
flowers  at  all  times  of  the  day. 

The   collection  of    pollen   was  witnessed  several  times, 

*  Pronuba  maculata,  var.  aterrima,  n.  var.  Characters  of  the  species,  but 
the  chitinized  parts  smoky  brown,  and  the  scales  of  a  dead  black  color 
throughout,  or  a  few  pale  ones  near  the  tips  of  the  primaries.— Living  as 
a  larva  in  the  forming  seeds  of  Hesperoyucca  Whipplei,  var.  graminifolia, 
the  flowers  of  which  are  pollinated  by  the  female  imago.  In  the  foot- 
hills immediately  north  of  San  Bernardino,  California,  April,  189:!. 
Types  deposited  in  the  Entomological  collections  of  the  National  Museum, 
the  Agassiz  Museum  and  the  California  Academy. 


FURTHER    STUDIES    OF   YUCCAS.  217 

under  a  cloudless  sky,  the  first  time  nt  about  noon.  Flying 
into  a  flower,  the  rnoth  runs  about  the  bases  of  the  stamens 
after  the  manner  of  other  species,  then  quickly  clambers 
upon  the  inner  side  of  a  filament,  and,  with  the  tentacles 
extended  over  the  pollinia,  drags  first  one  and  then  the  other 
out  of  the  anther  cells,  pressing  them  together  under  the 
throat,  and  subsequently  compacting  the  mass  together 
much  as  yuccasella  does  the  powdery  pollen  of  other 
Yuccas,  so  that  the  ball  finally  consists  of  as  many  as  ten 
or  a  dozen  pollinia.  So  quick  and  energetic  are  the  motions 
by  which  the  pollinia  are  removed,  that  the  stamens  are 
often  shaken  quite  violently,  as  I  have  before  noted  in  the 
more  nervous  attempts  of  yuccasella.  Oviposition  and 
pollination,  which  were  repeatedly  witnessed,  are  performed 
exactly  as  by  the  maculate  moth,  the  very  slow  movement 
in  the  latter  operation  being  quite  as  striking. 


The  relationship  of  the  Yuccas  to  one  another  and  to 
their  pollinators,  the  Pronuba  moths,  would  be  far  more 
intelligible  if  we  could  trace  their  history  back  even  a  short 
distance  into  the  later  geological  time,  because  as  Yuccas 
and  Pronubas  both  are  undoubtedly  of  recent  origin ;  but 
as  was  pointed  out  in  the  Third  Report  of  the  Garden,  this 
is  as  yet  impossible,  since  no  certainly  identifiable  Yuccas 
exist  in  even  the  latest  deposits,  though  plants  bearing 
more  or  less  resemblance  to  them  occur  far  back  in  the 
geological  epoch.  In  his  paper  so  frequently  referred  to  in 
the  foregoing  pages,  Professor  Eiley  has  called  attention 
to  the  ancient  type  of  vegetation  represented  by  the  tree 
Yuccas.  This  is  particularly  true  of  Y.  brevifolia,  which 
in  aspect  resembles  restorations  of  the  Carboniferous 
Lepidodendron  more  nearly  than  any  other  form  of  recent 
or  fossil  tree  with  which  I  am  acquainted.  The  other 
arboreous  Yuccas  are  more  like  the  Dracaenas  in  habit,  but 
the  latter  also  belong  to  an  antiquated  type. 

Though  no  single  species  extends  across  the  continent, 


215  MISSOURI    BOTANICAL    GARDEN. 

the  Yuccas  occur  in  practically  unbroken  continuity  from  the 
Atlantic  coast  in  the  vicinity  of  Fortress  Monroe  to  Florida, 
and  across  the  Southwest  and  Mexico  to  California  in  the 
neigborhood  of  Monterey,  Y.  glauca  reaching  well  up  on 
the  upper  Missouri  River,  and  Y.  baccata  following  the 
Rocky  Mountains  northwards  into  southern  Colorado. 
From  this  it  may  be  inferred  that  they  have  become 
specifically  differentiated  at  a  comparatively  recent  date, 
an  inference  which  is  supported  by  the  fact  that  notwith- 
standing various  dissemination  contrivances  which  may  be 
held  to  be  of  still  later  acquisition,  all  of  the  species 
except  the  distinctively  West  Coast  brevifolia  and  Whipplei 
may  be  broadly  classed  under  the  same  type.  The  occur- 
rence of  so  many  species  of  the  same  floral  type,  and  of 
what  may  be  called  modern  habit  of  growth,  over  a 
common  geographical  area  in  the  southern  part  of  the 
continent,  while  the  apparently  ancient  brevifolia  is 
restricted  to  the  desert  region  in  or  adjacent  to  California, 
and  the  seemingly  more  highly  differentiated  Hespero- 
yuccas  occur  only  in  the  mountains  near  the  latter  region, 
though  each  has  its  specific  Pronuba  quite  different  from 
the  one  associated  with  the  Eastern  Yuccas,  would  lead  one 
to  surmise  that  the  geological  record,  if  it  had  been  pre- 
served, would  show  that  the  first  of  the  Yuccas  were  of 
wide  distribution,  probably  extending  across  the  continent 
on  the  higher  parallels  while  the  northern  climate  was  less 
rigorous  than  it  now  is,  but  receding  to  the  south  under  the 
advancing  glacial  cold.  Indeed  it  seems  reasonable  to 
suppose  that  the  ancient  type  as  represented  in  brevifolia., 
with  an  equally  ancient  type  of  Pronuba,  has  persisted  in 
the  Pacific  region  throughout,  perhaps  owing  to  the  series 
of  circumstances  which  have  led  to  the  preservation  of  the 
Sequoias  in  the  same  region,*  while  the  more  widely 
distributed  species  became  differentiated  and,  with  their 
pollinator,  passed  to  the  south  under  new  conditions. 

*  See  Gray,  Presidential  Address,  Dubuque  meeting  American  Asso- 
ciation for  the  Advancement  of  Science,  — Proceedings,  xxi.  1. 


FURTHER   STUDIES    OF   YUCCAS.  219 

All  of  the  Yuccas  agree  in  the  possession  of  a  general 
liliaceous  type  of  flower,  and  in  having  compound  pistils 
with  a  stylar  canal  and  septal  nectar  glands.  The  latter 
characters,  however,  pertain  to  a  considerable  group  of 
Monocotyledons,  and  evidently  antedate  the  evolution  of  the 
Liliacese  as  an  order.*  If  my  view  is  correct,  each  of  these 
characters  came  to  Yucca  in  a  fairly  advanced  state  of 
development,  from  an  earlier  type  of  monocotyledonous 
plants.  In  brevi folia  or  its  immediate  ancestors,  as  well 
as  in  the  eastern  Yuccas,  the  stylar  canal  appears  to  have 
been  extended  and  amplified  at  top  through  the  marginal 
union  of  erect  stigmatic  lobes,  so  as  to  form  the  peculiar 
stigmatic  chamber  into  which  the  pollen  must  be  thrust 
in  order  to  properly  develop  its  tubes  and  fertilize  the 
ovules. 

Originally  having  spreading  stigmas,  we  may  assume  that 
the  progenitors  of  the  Yuccas  were  slightly  specialized  ento- 
mophilous  flowers,  pollinated  by  hymenoptera,  diptera  or 
lepidoptera,  which  were  attracted  by  the  secretion  of  the 
septal  nectar  glands.  With  the  consolidation  of  the  stigmas, 
however,  insects  visiting  the  flowers  for  this  nectar  became 
ineflicient  pollinators,  as  may  be  seen  when  such  insects 
enter  the  flowers .  of  the  existing  Yuccas  for  the  little 
nectar  still  produced ;  hence,  with  an  economic  reduction 
of  the  secretion  of  these  glands,  may  have  come  an  addi- 
tion of  their  function  to  that  normally  borne  by  the  stigma, 
in  an  increase  in  its  secretion,  so  that  the  visitors,  laden 
with  pollen  unconsciously  accumulated  while  in  the  flower, 
should  further  visit  the  stigma  on  which  some  of  their 
burden  might  be  rubbed  while  they  were  feeding.  Dur- 
ing this  stage  of  its  evolution  the  plant  appears  to  have 
proved  especially  attractive  to  some  small  moth,  perhaps 


*  For  a  stylar  canal  in  Agave  see  Danielli,  Studi  sull'  Agave  Ameri- 
cana, Florence,  1885,  59,  pi.  10 ;  George  and  Wittmack,  Gartenflora,  1892, 
278,  f .  55,  but  incomplete.  References  to  the  principal  papers  on  septal 
nectar  glands  are  given  in  a  short  note  by  myself  in  the  Bulletin  of  the 
Torrey  Botanieal  Club,  1886,  135. 


22Q  MISSOURI    BOTANICAL    GARDEN. 

fond  of  nectar,  and  with  phytophagous  larvae,  which  is  to 
be  regarded  as  the  progenitor  of  the  Pronubas  and  their 
close  relatives  of  the  genus  Prodoxus,  the  history  of  which 
has  been  so  well  summarized  by  Professor  Eiley  in  the 
Third  Garden  Report.  Whether  the  first  Prodoxids  were 
also  pollen  feeders,  so  that  their  mouth  parts  became 
accidentally  laden  with  pollen  between  their  visits  to  the 
stigma  in  search  of  its  secretion,  I  cannot  surmise.  As  my 
friend  Dr.  Lind  has  suggested,  they  may  have  learned  to 
collect  this  substance  and  deposit  it  in  the  stigma  through  an 
instinct  such  as  prompts  the  mud-dauber  to  place  its  prey 
about  the  point  where  its  eggs  are  laid,  or  the  bee  to  deposit 
honey  and  pollen  where  it  can  be  used  by  the  lame,  as 
though  its  young  were  to  be  directly  nourished  by  the  pol- 
len. At  present,  however,  the  act  appears  to  be  strictly 
voluntary,  without  food  compensation,  and  entirely  con- 
nected with  the  fertilization  of  the  ovules.  The  fact  that 
the  septal  glands  of  the  several  species  still  secrete  at  least 
a  small  amount  of  nectar  may,  as  Riley  believes  to  be  the 
case,*  depend  upon  the  indirect  utility  of  this  secretion  near 
the  base  of  the  flower  in  drawing  insects  other  than  Pronuba 
away  from  the  stigma ;  or,  as  I  am  inclined  to  think,  it  may 
merely  indicate  that  the  abortion  of  the  glands  is  not  yet 
complete.  The  glands  themselves  need  not  be  expected  to 
disappear  or  to  be  reduced  in  size  to  an  extent  correspond- 
ing with  their  loss  of  activity  under  this  latter  supposition, 
for  their  persistence  does  not  itself  imply  any  drain  on  the 
forces  of  the  plant,  since  they  represent  mere  clefts  in  the 
connate  walls  of  the  carpels  which  have  united  to  make  the 
compound  Yucca  ovary.  It  is  possible,  however,  that  the 
rather  abundant  stigmatic  secretion  is  not,  as  I  have  sup- 
posed, now  being  reduced  from  a  still  more  abundant 
quantity  that  once  served  as  true  nectar,  —  and  this 
assumption  of  a  former  nectariferous  function  of  the  stigma 
would  be  superfluous  if  Dr.  Lind's  theory  were  correct,  — 


*  i.e.  no 


FURTHER   STUDIES    OF   YUCCAS.  2?1 

since  the  Agaves,  with  an  entirely  different  sort  of  pollina- 
tion, possess  an  equally  copious  stigmatic  secretion. 

The  Hesperoyuccas,  represented  by  Whipplei  and  its 
variety,  appear  to  have  undergone  a  greater  adaptation 
to  general  pollinators  than  the  true  Yuccas.  Retaining 
the  stylar  canal  and  septal  glands  of  the  prototype, 
they  have  acquired  a  capitate  stigma  through  the 
consolidation  of  the  spreading  lobes,  the  small  stio1- 
matic  papillae  of  other  species  becoming  lengthened  as  a 
means  of  catching  pollen  adhering  to  visiting  insects.  On 
a  few  pistils,  one  of  which  is  represented  in  the  appended 
figure,  the  stigma  is,  in  fact,  separated  into  its  carpellary 


DIALYSIS  OF  HK8PEROYUCCA  STIGMA,  X  2. 

segments,  each  of  which  is  strongly  revolute.  Similar 
instances  of  dialysis  have  also  been  observed  in  the  true 
Yuccas,  and  these  teratological  specimens  represent  pretty 
nearly  what  I  suppose  to  have  been  the  original  form  of 
stigma  in  the  ancestors  of  the  Yuccas.  The  pollen  grains 
may  be  assumed  to  have  become  somewhat  viscid  as  a  means 
of  surer  attachment  to  visitors  which  did  not  go  deliber- 
ately to  the  anthers,  and  I  am  inclined  to  look  on  their 
agglutination  into  crude  pollinia  as  a  result  of  this,  —  per- 
haps intensified  on  the  return  of  the  plant  to  exclusive  Pro- 
nuba  pollination, — rather  than  an  original  provision  for 
their  bodily  removal  by  other  pollinators.  These  plants  may, 
therefore,  have  branched  off  from  the  earlier  Yuccas  after  a 
certain  dependence  on  Pronuba  had  been  formed,  perhaps 


222  MISSOURI    BOTANICAL    GARDEN. 

acquiring  their  more  general  adaptations  because  of  separa- 
tion from  Prodoxids,  and  readjusting  themselves  to  their 
former  pollinators  on  again  coming  within  their  reach ;  and 
I  am  disposed  to  think  that  this  is  the  case,  rather  than  to 
assume  that  the  generalization  antedates  their  first  asso- 
ciation with  Pronuba. 

The  evolution  of  the  Pronubas  has  presumably  gone  hand 
in  hand  with  the  adaptation  of  the  Yuccas  to  their  services 
in  pollination,  and  has  been  sketched,  in  its  essential  feat- 
ures, by  Professor  Eiley.  It  is  interesting  to  observe  that 
one  species,  P.  yuccasella,  accompanies  the  true  Yuccas  of 
the  most  differentiated  type  across  the  continent  from  the 
south  Atlantic  states  to  southern  California  (and  undoubt- 
edly the  peninsula),  and  that,  as  the  pollinator  of  Y.  baccata, 
it  occurs  in  California  associated  with  P.  synlhetica  and  P. 
maculata  and  its  curious  black  derivative,  which  pollinate 
respectively  the  archetypal  Y.  brevifolia  and  the  greatly 
differentiated  Hesperoyuccas,  thus  strengthening  the  in- 
ference that  the  latter  two  are  primarily  Pacific  types,  while 
baccata  in  its  present  form  is  an  immigrant  from  the  East, 
which  has  been  accompanied  by  the  common  pollinator  of 
the  eastern  species. 

In  a  paper  read  before  the  American  Association  for  the 
Advancement  of  Science  at  Rochester,  in  August,  1892, 
Professor  Smith  has  shown  that  the  curious  tentacles  used 
by  the  moth  in  pollinating  the  Yucca  flowers,  occupy  a 
position  similar  to  that  of  the  palpif  er  on  the  maxillse  of 
other  groups  of  insects,  and  so  is  disposed  to  homologize 
them  with  those  parts.  As  Professor  Cope  has  suggested 
to  me,  a  fuller  knowledge  of  the  embryology  of  lepidoptera 
may  show  the  general  prevalence  of  similarly  situated 
processes  in  the  early  differentiation  of  the  maxillae,  and 
thus  remove  the  only  valid  objection  that  I  see  to  Professor 
Smith's  conclusions,  the  isolated  occurrence  of  these 
appendages  in  the  group  of  lepidoptera.  At  present  they 
are  known  in  a  developed  form  only  on  the  females  of 
Pronuba,  and  as  rudiments  on  the  males  of  that  genus  and 


FURTHER   STUDIES   OF   YUCCAS.  223 

in  the  related  genus  Prodoxus.  The  occurrence  of  such 
rudiments  in  Prodoxus,  however,  is  very  interesting  from 
an  evolutionary  stand-point,  for  it  points  to  the  inference 
that  these  moths  are  retrogressions  from  the  Pronubas, 
rather  than  a  nearer  approach  to  the  common  parents  of 
both.  

The  three  types  of  fruit  on  which  the  primary  classifica- 
tion of  the  true  Yuccas  rests,  correspond  with  three  modes 
of  dissemination  in  the  genus.  About  half  of  the  recog- 
nized species  have  sweet,  edible,  pulpy  fruits;  two  have  in- 
dehiscent  fruits  similar  to  the  preceding  during  their  early 
development,  but  'dry  at  maturity;  and  the  remainder, 
including  nearly  one  half  of  the  true  Yuccas,  and  the  Hes- 
peroyuccas,  have  dehiscent  dry  capsules.  All  of  these 
fruits  agree  in  their  type  of  structure,  as  might  be  ex- 
pected from  the  general  uniformity  in  the  parts  of  the 
ovary  in  the  several  species.  In  all  of  those  I  have  been 
able  to  study  during  their  development,  the  inner  part  of 
the  ovarian  wall,  corresponding  to  the  superior  face  of  the 
infolded  carpellary  leaves,  becomes  more  or  less  firm,  the 
walls  of  its  cells  being  thickened  and  deeply  pitted,  while 
the  outer  part  is  green  and  fleshy,  and  no  doubt  takes  part  in 
the  assimilative  work  of  the  plant.  In  the  Sarcoyuccas, 
this  outer  part  becomes  much  thickened  and  quite  succulent 
and  sweet  toward  maturity,  assuming  a  yellowish  or  pur- 
plish color  and,  in  short,  undergoing  the  usual  ripening 
process  of  baccate  fruits.  The  seeds,  meantime,  in  most  of 
these  species,  are  immediately  surrounded  and  protected  by 
the  firm  inner  layer  previously  mentioned,  which  suggests  in 
texture  and  function  the  core  of  an  apple,  and  in  which 
the  seeds  rattle  with  considerable  noise  when  the  fruit  is 
shaken.  The  pulp  is  easily  removed  from  this  core,  which  is 
usually  shaped  to  the  convexity  of  the  thick  seeds,  so  that 
when  denuded  it  bears  quite  a  strong  superficial  resem- 
blance to  a  small  ear  of  corn,  a  number  of  interspersed  pale 
and  undeveloped  seeds,  causing  a  mottling  suggestive  of 


224 


MISSOURI   BOTANICAL    GARDEN. 


the  "  squaw  corn  "  of  the  Indians.  In  aloifolia,  where  the 
pulp  becomes  almost  black  throughout,  the  very  slight  core 
also  at  length  becomes  pulpy.  These  fruits  are  well  adapted 
to  dissemination  by  fruit-eating  animals,  especially  birds,  the 
linn  core  suggesting  that  the  pulp  only  is  swallowed,  the 
seeds  being  thrown  away;  but  I  do  not  know  of  any 
recorded  observations  on  their  dissemination. 

The  Clistoyuccas,  with  dry  indehiscent  fruits,  comprise 
the  curious  tree  Yucca  of  the  deserts,  Y.  brevifolia,  and  a 
single  eastern  species,  Y.  gloriosa.  Though  frequent  in 
cultivation,  the  latter  is  one  of  the  least  known  Yuccas,  and 
its  fruit  has  been  observed  rarely.  All  that  I  can  learn  of 
it  points  to  the  conclusion  that  its  fruit  is  of  the  Sarcoyucca 
type  with  rather  thin  seeds  and  suppressed  development  of 
the  exocarp,  suggesting  a  retrogression  from  aloifolia;  but 
nothing  can  be  said  as  to  its  dissemination.  Y.  brevifolia, 
however,  differs  from  all  of  the  other  known  species  in 
having  a  very  thick  exocarp,  corresponding  to  the  pulp  of 
the  preceding  group,  but  dry  and  spongy  at  maturity. 
The  fruits  of  this  species  fall  quickly  after  ripening,  either 
by  a  distinct  disarticulation  or  because  of  the  brittleness  of 
the  pericarp  at  base,  and  their  rounded  form  and  very  light 
specific  gravity  render  them  well  developed  ' '  tumble 
fruits,"  and  point  to  their  dissemination  over  the  dry 
sands  of  the  desert  by  aid  of  the  strong  winds  which  prevail 
there,  the  seeds  being  liberated  ultimately  by  the  breaking 
of  the  fragile  pericarp.  Although  brevifolia  appears  to  be 
the  least  advanced  of  the  Yuccas  in  its  general  development, 
I  am  disposed  to  look  on  this  adaptation  of  its  fruit  to 
wind  dissemination  as  a  special  acquisition,  rather  than 
regard  it  as  representing  the  original  type  of  Yucca  fruit ; 
yet,  so  far  as  the  facts  are  known,  it  might  equally  well 
be  held  to  be  an  advance  on  an  earlier  unspecialized  fruit, 
or  a  retrogression  from  the  baccate  type. 

In  the  capsular  species,  the  green  exocarp  dries  down  to 
a  rather  thin  layer  at  maturity,  and  the  core,  with  this 
adherent  film,  dehisces  through  the  true  septa,  and,  for  a 


FURTHER    STUDIES    OF   YUCCAS.  225 

certain  distance  from  the  top,  through  the  backs  of  the 
several  carpels  (PI.  22).  The  seeds  of  all  of  these  species 
are  thin  and  flat  and  the  capsules  are  erect,  so  that  the 
adaptation  to  the  scattering  of  the  former,  a  few  at  a  time, 
by  gusts  of  wind,  is  that  usual  in  capsular  fruits  of  this 
kind.  It  is  interesting  to  note  that  Whipplei  and  its 
variety,  representing  the  aberrant  group  of  Hesperoyuccas, 
possess  the  thin  margined  seeds  of  the  capsular  true 
Yuccas,  but  the  capsules  dehisce  to  the  base  in  a  loculicidal 
manner,  that  is,  through  the  false  partitions,  the  tough 
core-like  tissue  of  which  is  arranged  in  a  transverse  lace- 
like  structure  (PI.  23).  Though  dissemination  depends 
on  the  wind  in  both  cases,  the  seeds  of  the  capsular  true 
yuccas  are  lifted  out  of  the  pods  by  the  wind  dipping 
into  the  opened  top  of  the  cells,  while  in  Hesperoyucca 
they  are  removed  by  puffs  of  air  entering  at  the  side  through 
the  lace  work  across  the  deep  lateral  clefts,  in  the  manner 
beautifully  described  for  Lilium  in  an  anonymous  article  in 
the  Bulletin  of  the  Torrey  Botanical  Club,  i.  p.  46,  and 
well  known  in  the  basket  fruits  of  some  Aristolochias,  etc. 


EXPLANATION  OF  PLATES  ILLUSTRATING  YUCCAS  AND  THEIR 
POLLINATION. 

Plates  1-2,  y.  Guatemalensis,  flowering  and  fruiting  plant  at  the 
Garden. 

Plate  3,   Y.  Schottii,  near  Benson,  Arizona. 

Plate  4,  Y.  australis,  near  Sierra  Blanca,  Texas. 

Plate  5,  Y.  australis,  —  a  specimen  from  the  same  region,  cultivated  at 
the  Garden. 

Plates  6-9,  Y.  brevifolia,  about  Hesperia,  California. 

Plate  10,  Y.  elata,  near  Benson,  Arizona. 

Plate  15,  r.  elata,  descending  axis,  twaand  a  half  years  from  the  seed, 
one-half  size,  —  the  principal  growth  made  in  the  season  when  figured, 
(after  Engelmann) . —  Y.  filamentosa,  germination,  X^« 

Plate  16,  Hesperoyucca  Whipplei,  at  Summit,  California. 

Plate  17,  H.  Whipplei,  var.  gramimfolia,  at  Arrowhead  Springs,  Cal. 

Plate  18,  Y.  aloifolia.—  1,  Flower,  natural  size;  2,  pistil  and  stamens, 
X2 ;  3,  sections  of  pistil  at  points  marked  by  dotted  lines,  X  2. 
Y.  Treculeana.—l,  flower,  natural  size  (after  a  drawing  by  Mrs.  H.  J- 
Webber) ;  5,  pistil  and  cross  sections,  X2- 


226  MISSOURI   BOTANICAL    GARDEN. 

Plate  19,  r.  Quatemalensis.  —  1,  Flower,  natural  size;  2,  pistil  and 
stamens,  X2  5  3>  sections  of  pistil  at  points  marked,  X2  5  *>  f ully  grown 
but  green  fruit,  natural  size;  5,  seed,  X2- 

Plate  20,  Y.  baccata. —  1,  Flower,  natural  size ;  2,  pistil  and  exceptionally 
long  stamens,  natural  size;  3,  pistil  (the  upper  part  in  longitudinal 
section),  and  cross  sections,  X25  4>  enlarging  ovary,  showing  Prouuba 
punctures,  natural  size;  6,  cluster  of  fruits,  perforated  by  escaping 
Pronuba  larvae  (after  a  photograph  taken  near  San  Diego,  Cal.,  by  Parker 
and  Parker),  reduced. 

Plate  21,  Y.  brevifolia,  —  1,  Flower,  at  time  of  pollination,  natural  size; 

2,  pistil  in  longitudinal  section,  and  cross  sections  at  points  marked,  X2; 

3,  Pronuba  synthetica,  X3  5  *>  oviposition  of  moth,  natural  size ;  5,  head 
of  laden  $?,  X*0;  6,  young  larvae  in  developing  fruit,  reduced  one-half; 
7,  ripened  but  rather  small  fruit,  from  which  the  larvae  have  escaped, 
natural  size. 

Plate  22,  Y.  filamentosa.—l,  Flower,  natural  size.  r.  elata.—2,  pistil 
and  stamens,  and  cross  sections  of  pistil,  X2 ;  3,  dehiscent  capsule,  per- 
forated by  escaping  larvae,  natural  size.  Y.  glauca,  var.  stricta.— 4,  pistil 
and  stamens,  and  cross  sections  of  pistil,  X2«  6>  Pronuba  yuccasella, 
X3. 

Plate  23,  Pronuba  maculata,  var.  aterrima.  —  1,  Laden  9,  X3;  2>  nead 
of  same,  X10-  Pronuba  maculata.  —  3,  laden  £,  X3>  aQd  venation  of 
wings ;  4,  pollination.  Hesperoyucca  Whipplei.  —  5,  flower,  natural  size  ; 
6,  longitudinal  section  of  pistil,  and  cross  sections  at  points  marked, 
X2 ;  7,  stamen,  adnate  to  base  of  petal,  X2  >  8,  section  of  ovary  punc- 
tured in  oviposition,  X2  >  9,  small  capsule,  dehiscent  through  the  false 
septa,  natural  size. 

Unless  otherwise  stated,  the  plates  were  drawn  by  Miss  Johnson,  from 
photographs  or  studies  by  the  author,  or  are  reproductions  of  photographs. 


Since  the  preceding  pages  were  electrotyped,  the  paper  by  Professor  J. 
B.  Smith,  on  the  maxillary  tentacles  of  Pronuba,  referred  to  on  p.  222, 
has  been  printed  in  Insect  Life,  v.  161,  Jan.  1893. 


PRESS  OF  Nixon-Jonas  PEWTIMO  Co.,  215  PINK  STREET,  ST.  Louis,  Mo. 


PLATE  l. 


YUCCA  GUATKMALEXSIS. 


KEPT.' Mo.  HOT.  GAKD.,  1893. 


YUCCA  GUATEXIALEXS1S. 


Private  lib  iry  of 
J.ELIOT  CO1T 
Please  return. 


KEPT.  Mo.  EOT.  GARD.,  1S93. 


YUCCA    SCFIOTTII. 


KEPT.  Mo.  Box.  GARD., 


PLATS  t. 


YUCCA   AUSTIIALLS. 


KEPT.  Mo.  Box.  CARD., 


YUCC.V    AUSTRALIS. 


KEPT.  Mo.  HOT.  GARD 


PLATE  6. 


YUCCA   BREVIFOLIA. 


REFT.  Mo.  EOT.  GARD.,  1893. 


YUCCA    BltEVIFOLIA. 


KEPT.  Mo.  Box.  GARD., 


YUCCA    BREVI  FOLIA. 


REFT.  Mo.  Box.  GARD.,  1833. 


REPT.  Mo.  Box.  GAUD. 


PLATE  10. 


YUCCA    KLATA. 


REFT.  Mo.  EOT.  CARD.,  1893. 


PLATE  15. 


YUCCA   ELATA    AND   FILAMENTO8A. 


Private  library  of 
J.ELIOT  CO  IT 
Please  return. 


KEPT.  Mo.  Box.  <iARD.,  1893. 


PLATE  i<;. 


HESPEUOYUCCA   WHIPI'LEI. 


UEPT.  Mo.  HOT.  GAKD.,  18»3. 


PLATE  17. 


HESPKKOYUCCA    VV11IPPLKI,    VAK.    GRAMIMFOLI^. 


KEPT.  Mo.  Box.  CARD.,  1893. 


1M,ATK   1,- 


1 


YUCCA  ALOIFOLIA  AND  TRKCULEANA. 


KELT.  Mo.  I'.OT.  GAUD.,  1803. 


YUCCA  GITATKMALENSI3. 


KEPT.  Mo.  UOT.  GARD. 


PLATE  20. 


YUCCA   I5ACCATA. 


KEPT.  Mo.  DOT.  GARO.,  1893. 


YUCCA  BREVIFOLIA. 


KEPT.  Mo.  DOT.  GARD.,  1893. 


YUCCA,  §  CHAENOYUCCA. 


KEPT.  Mo.  HOT.  GAKD., 


PLATE  -.>:!. 


II 


HESPEKOYUCCA  WHIPI'LEI,  AND  VAKIKTV. 


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